Rebreed 75%? Looking at OU, there are only 3 out of 42 mon, or a mere 7%, that almost 100% prefer to have H.A over their normal abi, and so you will want to rebreed them:
1) Dragonite with Multiscale
2) Mamoswine with Thick Fat (although, even Oblivious is useful for a sash lead)
3) Gliscor with Poison Heal
There are other Pokemon which has useful abilities, but can't be said to be always better than the normal abi, e.g. Starmie can use either Natural Cure or Analytic, Excadrill with either Sand Rush or Mold Breaker, or Conkeldurr with all three usable abilities, etc.
This means the release of hidden abilities will only enrich the game content, and hardly a replacement of old contents.
So, I just don't see the need for untradeable HA pills per ur suggestion, as they will dilute the value of hunting for H.A. mon in the dungeon.