It’s not as major as it looks. The math is very transparent. You could literally get rid of ability scores, and replace them with “Primary, Secondary, and Tertiary, Competence”, and change nothing else about the system. It’d make for a long document, but the work wouldn’t be complex, mostly just repetitive and time intensive.
Another option would be to let each character choose their primary ability score from the normal 6, with the note that physical attack score and Spellcasting score can not be the same, unless a feature allows it (ie, anyone but Hexblades pretty much still has two “main” stats).
This could either be restricted to physical stuff requiring a physical score and magic stuff requiring a mental score, or not, at a group’s preference. I’m fine with Strength wizards and Con sorcerers and Cha fighters, others won’t be.
I absolutely will not be hashing out details of either idea in this thread, so please don’t try to pick them apart. The point is simply that ability scores changing doesn’t require an overhaul of every system, which is what I imagine when someone talks about redesigning completely, or whatever the exact phrase was.