The 6 attributes are the most sacred of the D&D legacy elements. But what if we just eliminated them entirely? What if we just used skills, proficiencies, feats, etc to define what a character is good at mechanically?
Could D&D be D&D without ability scores? Would you play D&D without ability scores?
I've long said that with the addition of weapon specialization, NWPs/skills, feats, and all these other ways to differentiate characters, that attributes have become one of the least interesting ways of doing this differentiation. This is doubly so as attributes (at least in the classes most associated with them) have moved from a handy way to get a +10% bonus to a real and consistent bonus, to a major bonus, to an effectively required high score. This means that there are few if any weak fighters* or dumb wizards** or unwise clerics running around, and the best way to play a 12 Str fighter since 1975 has been to find a way to make their Str be not-12 (through ASIs, magic items that replace rolled stats, or strategic restarting with new characters/chances to roll stats).
*dex-based fighters being an exception, but one that just means there are two alternative scores to which you need one to be high.
**yes, yes, 5e you can theoretically make 8-int wizards work -- with some very specific niche builds.
That said, this has been mostly an argument against making attributes be an integral part of a class's basic gameplay architecture. If you could actually make a weak fighter or dumb wizard or the like (or just be able to put your most middling stat there and focus your high/low stats on your wizard's wisdom or your fighter's intelligence or the like) then suddenly attributes could be character-defining again. To do this, I would try making attributes only count for a few things (not class-role-definitional). Maybe just skills and related checks (jumping, climbing, etc.). Maybe saves as well, or even tangential class role stuff like encumbrance (just not to-hit and damage, etc.). This would mean you could reasonably play Taran the pig-keeper (from The Chronicles of Prydain) as a Str 8-10 boy knight-aspirant, or a Puss in Boots-style Int-based fighter or rogue, or similar.
Mind you, none of these require attributes to actually go away. However, I am suggesting that they don't matter overly much for various aspects of the game (the part where fighters hit things with swords and wizards cast spells to solve problems, etc.). Whereupon, I guess they become optional, if not actually requiring them. Whether you could then remove them and it still 'be D&D' is one of those subjective feelings-based things that are hard to pin down. Generally I'd leave them in with some kind of mechanical usefulness, but exactly what or how much, I am not sure.