Having only glanced over it, I think I'm going to say it will stack, unless "DM puts his foot down" (ie, if I see some nasty abuse w/ it, I'm going to nerf it back).
I'm an old school AD&D person, and the abuse gained from changing shape is just horendous in this edition (and it was already bad in previous editions). I'm a pretty staunch believer that Druids should be able to use this class ability (as they had it in AD&D too), but due to the wicked strength of it, the confusion it causes, and everything else I wanted to tone the abilities down.
Did I over-nerf them?
On the egoist idea - do you want to develop a unique power that takes its place? I'd work with you on that one.
Orange Ioun should stack. Anything that doesn't specify arcane or divine should work...
Oh, and UPD = UMD; I don't know what the RAW is on that one.
Psionics in general are rare in Faerun; I don't know if I'm going to enforce that, though.