It's not a new rule! Though after some discussion with the other judges, if it's possible to achieve a game that meets all of O2A2's requirements, we don't see why it couldn't be used to make a submission.
(I'm personally not familiar with how to strip down the engine to achieve such a thing though, so I can't advise on how to go about doing that ><)
If you're using the newer engines (RPGMaker MV and I think MZ does the same), there is a nifty feature where you eject all unused assets so only assets that appear in the game will be present (so no bloat). This not only saves on filesize, but would be able to meet the requirements of O2A2 if you were to make it into a visual novel. This is a feature used when you pack your game, where you checkmark exclude all unused assets ^^
