Ok, Mike Mearls here is a way to manage the inevitable crushing system bloat of 5e without it making the whole thing both byzantine yet also somehow bland.
We all know player options sell more than GM options. So any corporation is going to end up overproducing these and jamming out splatbook after splatbook with crap you can add to your character. This will both increase the amount of complexity and powergaming and yet also, somehow, make everything a bit more vague and woolly.
A game where everyone playing is a weird living crystal of some kind might actually be kind of good. But a game where a living crystal teams up with a Minotaur and a Doppelgänger and a Hill Dwarf probably won’t be. It takes a kind of pressure off the creation of the world. None of these things can be truly strange or 'other'. The charge of their discovery is lost. The fusion-like power you get when you introduce something utterly unpredictable into a coherent world system is lessened.
But this is a tide in the hearts of men and especially in the hearts of Americans. Because in America everybody must have access to every choice. Taking away or limiting choice can never be considered a good thing. Oh, small groups of individuals might cling together on a temporary basis to play games with highly-focused limited options. But doing this makes them perverts and they know it. They will always be the minority for such a thing works against the spirit of the land. Why can't you be a Ninja in FauxEurope? WHY? THIS IS AMERICA AND YOU CAN BE ANY DAMMN THING YOU WANT.
In the same way, for a variety of reasons, people, and Americans in particular, will never be entirely comfortable with the 'Other' as a powerful presence in serial fiction. The Borg can be terrifying once, but then you get a sad Borg, and a sexy Borg and a conflicted Borg who feels odd about being a Borg and Borg babies.
Can Orcs be 'evil'? It’s a stupid question in some ways but it will never ever be gone from the communal mind, partly because its the West* and partly because its America and you just said that an entire race/species can be evil. And it doesn’t matter how far the representation gets from reality, it nudges a wound in the nations soul. It will never be an entirely comfortable idea. There will always an exile Drow, there will always be a Noble Savage Orc there will always be a bad guy that it-turns-out-has-a-point-and-who-are-the-real-monsters-anyway-could-it-be-MAN?
And the corruption, or, in this case, blandification, or humanising of the 'other' makes for bland boring stories of adventure because the whole point of adventure, its central charge, is to come face to face with Something Else, something from Outside.
So, to recap.
1. Hasbro will be producing lots of Player-Facing stuff.
2. Everyone must have MAXIMUM CHOICE because FREEDOM.
3. The charge of the Other will always be lessened.
This is a way to ride that wave in the least frustrating way. Instead of turning the wheel of liberalism half-way round to its customary middle-volume position. Spin that motherfucker 360.
Instead of producing books about other worlds or realities where the Player Races are different but the Others are the same array, produce books from other moral worlds and cultural realities. Produce books from the perspective of these cultures where they are the heroes and we (and elves, dwarves and hobbits who are our aspirational shadow selves) are the other.
Lets look at how this might go.
Orcs, Goblins, Gnolls, maybe Thri-Kreen
Normal D&D is the points of light pressing out into the surrounding darkness like a spider web. Instead, this would be a collapsing natural world. A world of tundra, mountains, forests and ancient sacred deeps slowly being strangled by an encroaching and consuming civil order. The races that live here are not reaching out, but being pushed back in irregular patterns. They are martial, vital cultures who, yes, might eat a guy but it’s nothing personal.
Adventures are, instead of going into dungeons: breaking into villages and towns, and even cities in the end game. As well as dealing with monsters and all the usual D&D stuff. Treasure could be food or land. There could be multiple civilised peoples with different attitudes and a patchwork of old/new lands with different challenges.
'Monsters' sneaking through a semi-civilised area is like Heroes sneaking through the wilderness.
(If you want to be extra-sure to not offend the parents, make the evil empire extra evil, fascist, racist and nasty even to its own so when you take it on its all right really dad.)
Drow, Duregar, Svirfneblin, Myconid, Olm, Kua-Toa? Quaggoths?
Ok even with a lot of fudging this one is going to be a bit evil. But, all you need to do to make it acceptable is have the players face off against things that are even worse and do it in ultra-dangerous circumstances. World-conquering daemons, Mindflayer Crusades.
Cunning members of ancient hidden cultures battle and destroy immortal evils deep beneath the surface of the earth. Decadent but brilliant badasses pull mad intrigues against even-badder scum. Or just: a mixed group of low status adventurers put aside racial resentments and, to everyone’s surprise, become ultra-competent league of problem solvers. It would be a bit like mid-run Breaking Bad crossed with the A-Team.
Skeleton, Vampire, Revenant, Ghost? Lich? Mummy?
Skeletons level up into Skelton warriors and Death Knights, or become Liches if they get good enough at magic. Non-corporeal is tricky but could give them increasing abilities to affect the world as they get stronger. Basic spirit can level up through poltergeist, to shadow or ghost.
A city of the dead like Mievilles High Cromlech. Obsessive ritualised timeless society. Missions based on memories or sorrows or requests to retrieve particular relics and fragments of the dead. Down time periods take place over centuries, not years. Char Gen could be you are all made in the same dungeon by the same necromancer, then heroes attack.
THE BLUE WORLD
Tako, Triton, Merman, Sea-Elf?
(Ok I read through all the 'good' underwater player races and they are rubbish.(Except maybe Tako))
Ixitxachitl, Sayhuagin, Locathah.
No-one ever does the ocean as it is meant to be done and that’s because they treat it as a big dish. Like an alternate map, but underwater. It's a complex, fluid three dimensional flowscape. The real continents and nations are not the shape of the land beneath the sea but the currents and layers of the seas itself. The different trophic zones are like bordering countries, the great oceanic flows that bring warmth and cold around the globe are like continents.
Different races and cultures dominate different vectors and layers. Many of the cities move. Everyone underwater thinks of it as the 'real world' not as an addendum to the land. Because you would if you had access to the majority of the planet.
There are numerous deep-sea caves, so that solves that problem. Missions could be to the ruined palaces carved upside down under the arctic ice, to the lightless trenches, to the undersea volcanic borderlands where fire and water meet. Plus, numerous sunken cities. Floating cities built underwater and lost or abandoned, drifting, full of ghosts and a thousand years of accumulated clumped together history. Like undersea Space Hulks. The cursed city of Repak-Noh appears drifting silently on the borders of the Troposphere, before it inevitably falls back into the midnight zones and is lost for another millennia. Who shall investigate its gleaming portals? You. You shall. Underwater D&D, not as a holiday, but as the main game.
Ehhh, Githanki aaannd the other space/psionic ones? Shardminds? Ok this ones a bit of a reach.
I suppose your base is the realm of madness and dreams and reality itself is the dungeon. A nest of freezing time knotted space inhabited by strange beings.
Anyway. To sum up.
The point is that you could have all of these in the same world, but they would remain different and powerful to each other because the each inhabit a different kind of moral and experiential universe. Yes, you can do crossovers, but the dead are always strange to the living. The sea is always strange to the land. The 'savage' is always strange to the civilised.
They are all heroes but they are heroes inside their own worlds like everyone is, and the difference between those worlds lets you have difference and diversity whilst keeping them strange to each other, so when they show up in each others stories they are still reasonable monsters.
Kids are used to this because they know it’s from Warcraft and its ilk where everything is playable, yet separate.
Each would be a different kind of game, but all you would need for each one is a new players handbook. The basic engine underneath would remain the same. Maybe new ideas for missions and xp. And your items and treasures from one book can be the treasures and monsters for every other book.
*Yes I'm sure they have this kind of thing in the 'East' as well and that 'West' and 'East' are troubled concepts, thank you Richard.