Yep, exactly like Monstrosity from XI where you can fight against an alliance of players as your customized monster. While it isn't tiered like your idea, essentially your capped out monster would be customized to the point it may look like a Wamoura, but you fight like a mix of a behemoth, mandragora etc etc so the alliance doesn't know what to expect.
(Another reason I say XI still managed to do more than XIV.)
So actually, it'd be very easy for them to do..the question is..would they do something against the ARR norm? Monstrosity is fun as hell.
https://www.youtube.com/watch?v=ht-oiHa4_bs < Take for example.
Edited, Sep 5th 2015 7:47am by Theonehio