I'm old enough to remember when they had sub-abilities that split up things like strength into brute strength which added to attack and damage and an aspect of strength that leaned more into the endurance side of things. So everyone just maxed out their brute strength (or whatever it was called, too lazy to get my book).I thought I did but perhaps I was too vague. To me the most important D&D tradition is that you're an "[insert race/lineage] [insert level][insert class/subclass]" and that that is defining thing that's immediately going to tell people about how your character plays and and what they're about.
This is pretty different to a lot of other TT RPGs. Class, race, and level.
Beyond that I think there's a hell of a lot that's kind of up for discussion whilst potentially still being D&D. I'd love to see HP increase but by a much smaller amount per level, for example.
Stat-wise, I could honestly see losing Constitution. Not because I hate it, but because it doesn't add much. Almost everything it's for you could use STR for or just remove from the game. So I'm guessing I'm finding that the six stats tradition doesn't matter or that be equally happy with one of those stats changing.
I think the 6 ability scores are one of the traditions that work, although dex in the current iteration is far too good. I guess if we got rid of con people would have a reason to invest in strength.

I guess I was just trying to point out that I don't envy the developers because there will always be compromises. One person's tradition that makes the game what it is will be another person's sacred cow.
Bonus tradition I like: the relative lack of gunpowder. Which is really odd considering the technology level required for things like plate armor, I think it makes the game more fantastical.