I'm worried about attaching bonuses to class (and not just as a free floating 'thing' or balanced around an ancestories other abilities) because I feel that could cause unfortunate restrictions on how to play certain classes. Obviously, a lot of cases already have restrictions on how you play a class because at-least one ability score is quite important to play the class, but a lot don't force you to invest in two stats for sure (the whole SAD vs MAD) and some are quite flexible as of right now - Fighter and Paladin can be played as Strength or Dexterity based, for example (and I certainly wish the somewhat common homerule of Warlocks either being Charisma or Intelligence based was just the standarad).
I feel that attaching bonuses to class might not allow the flexibility - it is possible by the book but I can easily see decisions being that leads to Fighters only getting a +2 to Strength and a +1 to another, making Dexterity based fighters more difficult.
I also don't see this happening as it would likely make a 6e really incompatible with a 5e, and I think that compatibility is important not only business wise, but also community wise.