I think a simpler system would be to instead of using the ASI to improve a stat, it gave x amount of points that are used in the same way the point buy system is used. Then allow those points to be saved. For example, give 4 points at each ASI. Players could spend them on Stats, Feats, Skills, or save them up. The point buy table would have to be extended, but I believe that has already been done
9 = 1
10 = 2
11 = 3
12= 4
13 = 5
14 = 7
15 = 9
16 = 12
17 = 15
18 = 19
etc.
This would also be spent pre-racial bonuses just like normal point buy.
If this were done, players would most likely broaden their characters instead of gouging them, as most people cannot tolerate delayed gratification.
Say a character with a 15 max stat reaches 4th level (or its first ASI). It can now raise that stat to 16 (+3) and raise one of its low stats, or save that for its next ASI, or buy a very low valued feat like "Weapon Master".
This would also allow each feat to be assessed a value (which might vary for each game, for example, mounted combat feats would be rated low in CoS, but maybe higher in PoA).
While slightly more complex than 5e normal assumptions, it would have the effect of allowing more character flexibility while also implementing soft-caps.
