Perfect Memento has Akyu under the assumption that she's paid with human. Mei Ling also states to Reimu that she should have permission to eat humans and shrine maidens. So she really does seem to be quite carnivorous.
Me personally, I think Mei Ling MIGHT be an actual dragon god but doesn't realize it (and was probably sealed away, along with her memories. Possibly she may even be the original dragon that threatened to destroy Gensokyo, and Yukari sealed her away but lied to the historians by stating that she got the dragon pacified by pledging peace). The dragon symbolisms are already well documented (Hong meaning Dragon and on her hat, her rainbow spell cards, etc), but sometimes I wonder if her dreams about an epic youkai might actually be dreams about herself (Mei Ling's Hisoutenkan ending, she
), especially considering how serious business dreams tend to be in Touhou. Again, I say "might", since this is obviously mostly speculative.
....of course, it would also be a pretty hilarious joke by ZUN, that a youkai so disrespected and picked on might actually be the most powerful youkai of all.
Sadly, Iku doesn't really have any clues in her few VS quotes with Mei Ling, but maybe ZUN thought that'd be too obvious.