Oooh, now I get what you mean. I just finished reading your SU. Huh. I'll have to think this over a bit on my own, but assuming I'm okay with this concept I don't see why not.
There is one thing about your SU that caught my eye though: The appearance.Technically speaking, no character is supposed to look more like a human than a pokemon. Maybe it would help if I told you that a pokespirit wielder only fuses with one spirit at a time? They can freely shift between spirits, similar to a switching mechanic in a traditional battle. (Only it's more like a baton pass where all pokemon share the same HP ;P)