That will tend to mitigate the possibility of ability score increases that don't do anything, but doesn't help us resolve higher level ability bumps being relatively less useful to the character (assuming they've been bumping their primary 1-3 scores) while feats presumably get more powerful.
This would grant up to 16 ability scores increases (same as +1/+1 8 times) .....
Non-Casters are going to get 12 feats and casters 6, most likely between 3-15 levels.
Regarding the feat getting progressively less powerful, the simple exit to maintaining this is making the class concept (class+background) dependent on two primary stats (ala 4e); one from class and one from concept. As the main issue here is likely to be with non-casters, its far more likely these character concepts will be (should be) dependent on two stats anyway (basic fighter Str/Con; basic Rogue Dex/Cha).
It is worth also considering that is primarily a mechanism for balancing Basic and Standard/Advanced play, though the point is taken that a) different styles can be seen at the same table and b) a default progression will likely evole as being opitmal for when ability scores are taken (as shown above). Some of the great ideas here fail that test by making the feat inherently stronger between the play levels (ie feat vs something + feat), but the issue of dead level will be an issue for some.
I'd also like to see a built in feat like benefit for reaching 20 in a stat;
Str: Samson's Might (Double damage vs Inanimate Objects, Advantage on Athletics Checks)
Con: Perfect Health (Healing rate 1 step higher than campaign base, Advantage on Endurance Checks)
Dex: Cat's Grace (+2 Move, Advantage on Acrobatics Checks)
Int: Perfect Memory (Advanatge on Knowldege Checks)
Wis: Indomiable Will (Resistant to Charm), Clear Insight (Advantage on Insight checks)
Cha: Fascinate (like spell)
Finally, I'm also on board with base stats in gneral being lower. Currently, its easy to see starting characters at 18 or 19 in their primary stat, reaching 20 at 1st level with first selection at 3rd (the assumed non-basic starting level). I think this needs to be revised to 16/17 the starting max.