They should just make the final boss cutscene required. People will grouse and groan but they'll get used to it. If some really don't like it, they'll bail on the raid but people still want their tomes so the majority will stay and those people will get replaced like they do now when people bail on the raids they don't like. It should be required for everyone because the proble with only triggering on new people is that we could see new people kicked.

Usually on Aether if the call for cutscenes goes up, then the raid waits. I've even seen it in CT. It doesn't really take that long and it gives new people a good experience.