Either new specs like you said would be really fun, ORRRRR hear me out here…
Anyone ever play that old MMO Runes of Magic? was a failed pay to win wow clone. ONE great thing it did though was it had a really really fun dual class system. What would we think if for just either one season or for one xpac, WoW took on dual class like that??? could be a fun new change to make things really interesting again and give us something new, then they could go back to solo classes afterwards