This has some pretty major effects on gameplay. On balance, though, I think it’s probably going to be good for the game (and should decrease the randomness a bit because derandomized item sets are removed when used, meaning that you get a roughly constant gain from your Puissance expenditure over time if you’re spending it derandomizing its chests). It’s also likely to help the players who are behind catch up – if the leaders are spending Puissance fighting over chest contents, then everyone else will have more by comparison and be able to make their own moves.

Incidentally, the wording on this is fairly loose; I think it’s probably OK, but using rules-defined terminology, “Add the feature ‘Richardo approaches an average chest.’ to each of the rooms…” would make it much less debatable whether the proposal does anything at all.