From the issue page on the retroachievements github discussing this https://github.com/RetroAchievements/retroachievements-api-js/issues/46:
"I don't have a good answer to that. I am sure someone from engineering would be happy to talk with them. It's possible they need a very limited amount of data that is only served from one of the more read-intensive endpoints. If we know what their needs are, we could perhaps service something more lightweight and performant that wouldn't be under the umbrella of the partially-disabled stuff."
From the last few posts over the last few days on that issue, it sounds like they've reactivated most of what they intend to, currently, but some of the heavier api functions will not be returning any time soon. However, as per the quote above, they are willing to coordinate and work with you right now to get functional what they can.
