clearstream
(He, Him)
I was thinking through scenarios where a feat might feel costless (or undercosted) i.e. favoured from an optimisation perspective. This by no means is intended to dissuade you, as the mechanic seems reasonable overall to me. Some exemplary scenarios includeYou know, now that I think about it, the “reduce your two highest ability scores each by 1” rule could be applied as-written to all three methods, and it’s much cleaner and easier to explain than “If you use an array, pick from standard or reduced array and a feat. If you use point buy, spend 4 points on up to one Feat. If you roll use this special dice code.” It’s a very Gordian sort of solution, and that appeals to me quite a lot.
a. My two high rolls are odd numbers that I don't intend to increase through Race or an early ASI.
b. I use the 15, 15, 15, 8, 8, 8 array. A feat can be taken to make that 16, 14, 14, 8, 8, 8... which can be a better array mechanically.
c. I use the 13, 13, 13, 12, 12, 12 array. Taking a feat can make that 13, 12, 12, 12, 12, 12 which can be functionally just as good mechanically.
d. I use the 14, 14, 13, 11, 11, 10 array. Taking a feat can make that 13, 13, 13, 11, 11, 10. Playing human makes that 14, 14, 14, 12, 12, 11 which would be strong for any MAD choice.
It seems to me that players will likely opt into the feat when it feels undercosted. There are array + race choices that are mechanically identical even after reducing your two highest scores by one, and can be mechanically better if that is then turned into +1 onto an equal-high score. There are many fringe cases - like the human monk - that are mechanically identical even after reducing the two highest scores, and will be much stronger for having the feat.
So the predicted behaviour is that mechanically savvy players, or those who just stumble onto the right combination, will pick up the feat uncosted (from a mechanical perspective). One might suppose that they are really deferring the cost to the later ASI they take to make up for the lost points, yet such an ASI will likely funnel two points into the key ability, putting them in a better place anyway.