If you don't know what monstrosity was in FFXI, heres a link and video that sort of explains it:
http://wiki.ffxiclopedia.org/wiki/Category:Monstrosity
http://www.youtube.com/watch?v=MdWPeYEFqfM
Monstrosity was some of the most fun I ever had in FFXI, and although it never kicked off to full steam, it was really a well designed mode and felt almost like a whole game on its own. I found leveling monsters to see which one they would unlock was a lot of fun, and just being able to control things like the behemoth was always a blast. I think this would be a fun addition to FFXIV as well, and could even be used as a pseudo-open world pvp(Make your own boss fate? lol) like it was in FFXI. This mode could go hand-in-hand with the glamour system, by making sets of armor that could be obtainable from monstrosity for use in glamour, and could even have crafting materials, materia, and semi-good gear available and be an alternative to myth tier gear.
Thoughts?