I'd really see the end of RotZ plotline as a good 24-man raid.

1st part: Qu'fim Island and climbing up the Delkfutt's Tower with Kam'lanaut as the last boss.
2nd part: Run through Sanctuary of Zi'tah and Ro'maeve with mechanics involving the Full Moon fountain and some FFXI golem boss.
3rd part: Ru'Aun and Ru'Avitau. The Ark Angels, Eald'narche, Kirin.

Then again, all theses zones are super interesting on their own and I feel like it'd be a crime if they were only accessible as instanced zones. :P