Oh I like that.
Like RP wise they do get that stage, the companion and/or Dragon Form. BUT to have the art of it, yes, that's a good idea. They'll have to pay an extra fee of some sort. Like 250k sounds reasonable if they want it. Or they can get it commissioned from outside of the shop if they so desire as long as the artist is okay with them using it in the shop. :] Otherwise it would just be fanart. :3
But yessss, I like that a lot actually. It doesn't come with it, but it's an extra if you want to pay the money for the companion/dragon form piece! :3 GOOD THINKING YORU!!! *just wants to eat Yoru's brain all the time to obtain his smarts*