'Nother few ideas...
1) Less Heritages/Races
Yeeeah I get it. People like having a lot of variety in their heritages. But I find it mostly winds up in making the game a neverending cavalcade of animalfolks with a few planar entries along the way. And since every heritage has their own unique language, it dilutes the languages into a soup of nonsense where no one bothers to speak anything but common unless they're secretly talking trash with the one other person in the party who shares their language, or they meet an Elf King or something and the barbarian starts spouting Shakespearean English with iambic pentameter.
Languages are -fun- to play around with, when there's only a few to learn and you can be reasonably sure several of them will come up at different times in a campaign.
Though, to be clear, I'm just talking the core book. Individual Settings can, and should, have unique heritages for the setting. But Warforged and Changelings shouldn't become a core race on every world just because they're nifty in Eberron, you know? And I don't envy WotC's incoming attempts to bust Dark Sun wide open so everyone can play their favorite kitchen sink species....
I kinda wanna do a core set of heritages and then do the wider subraces thing more like A5e does with...
2) Cultures
Yup. Elves in the Underdark are Elves with an Underdark culture that gives them the stuff that makes them mechanically Drow. And you can also do it to Dwarves and then they'll be Duergar. And Gnomes for Svirfneblin. Etc etc etc. But also stuff like High Elf Culture for a Human to be a part of, too. Smaller number of heritages, broader quantity of cultures, more mix n' match ability.
And a fun thing for culture? It helps determine your lifespan. Oh, sure. A human has a life span that's shorter than an elf. But a human raised in high elf culture is gonna live a lot longer than a human raised on a farm. Similarly, an elf in a cosmopolitan city will live longer than their orcish neighbors in the same town, but not so long as the high elves of old. Call it diet, medicine, magic, whatever you like. I just think that's a fun thing.
Especially when elves raised in Goblin and Orc cultures die -really- young, but have a great time until then!
So heritage has a baseline life expectancy, and then culture extends or shortens it from there.
3) Languages
And, of course, the languages will be tied to the cultures! All the humans raised in Elf Cultures speak Elven. Or maybe something like "Ellowyn" as the elven language. And then the "Common" language is a regional/national thing. Wherever your game is set, that nation's language is the 'main' language, plus your cultural language. And, hey, however many points of Int mod, more languages.
But just to be tricky? Picking a non-Heritage culture (Like Circusfolk or Cosmopolitan) gets you a second regional/national language choice for your culture, rather than a heritage-specific language. Fewer languages, greater overlap of utility in having a given language.
Have a dedicated language for a few classes, too. Liturgical for the Clerics and Paladins. Druidic for the Barbarians, obviously. Thieves Cant certainly can... And then the language of the Arcane for the Mystical Types. But... not Draconic. More of a dead language that people don't use to communicate, anymore. Not something you swap to in order to negotiate with a giant rampaging firelizard.
4) 3 Up 3 Down for Stats.
10, 15, 10, 15, 10, and 15 are your starting stats. Roll 1d8. Add it to the 10, subtract it from the 15. Do it to the next set of 10 and 15. Then the last set. Congrats! There's your stats! It's possible to start with three 18s! And you'll also have three 7s. Every character has a total of +6 attribute modifiers. If you roll three 1s your stats are 14, 14, 14, 11, 11, 11. Three +2s for a total of +6. It gives the party the possibility of having a wide variety of stats, but keeps them overall balanced against each other.
The downside is that your friend with the hot dice that roll solid 18s for character creation (that may or may not be loaded with a tungsten plate) will have to slum it with the rest of us plebs, but that's a sacrifice I'm willing to make.
Of course, you can do 4d6 drop the lowest if you wanna. This is just the core stat generation method.
5) Multiclassing and Feats
Rather than being a Rogue 4, Barbarian 6, you'll just grab feats that grant you class abilities in addition to what you've got from your current class. Maybe get 5 feats over the course of leveling, and you can choose between grabbing class-feats or general feats.
It means balancing the multiclass feats against each other, and then the general feats against them... but I think it's plausible. I hope.