While undoubtedly more complex (and even more unlikely to be implemented), I think ASI should be changed to ASA "Attribute Score Adjustment," which would allow you to reduce any attributes you want (and recover the points you spent to buy them) and add another 6 points to spend; you could limit this to reducing an attribute by a maximum of 1. This will generally result in worse min/maxed builds at higher levels for those who take only ASA, but improved balanced builds. It would also allow you to drop odd attributes without respec.
I understand that might make min/maxers unhappy, so you could also drop the minimum for an attribute by 1 each time you take ASA. For example, you could reduce it to 7 when you took ASA the first time. to 6 if you took ASA a second time, and to 5 if you take ASA a third time (Rogues and Fighters could reduce to 4 if they took ASA a fourth time). The math for a min/max 17/16/15/8/8/8 build would get you a 18/16/16/8/8/7 at 4th Level, 20/16/16/8/6/6 at 8th Level (or 6th Level for a Fighter), and 20/18/16/7/6/6 at 12th Level (or 8th Level for a Fighter or 10th Level for a Rogue), assuming you were trying to replicate the most min/maxed attribute array currently possible. It's objectively worse in that context, but the penalty is only -1 worse for one, two, or three of the 3 attributes (which would each be 8 under the current rules) you were min/maxing, which shouldn't matter much because that's what min/maxing is. You can "keep up" with current rule min/max builds (on the maximum end) by dropping the floor by 1 each time. A 12th Level Fighter or Rogue would fare a little more poorly with a 20/20/16/6/6/4 instead of a 20/20/16/8/8/8, but I'd argue that's still fine for a min/maxed character (in the sense the player probably won't be mad).
