i could see that...but in a three stage boss fight ala Xemnas.
first phase: Nomura faces you in his casual attire, using the kingdom key as his main weapon. about halfway in, he switches out his weapon for another keyblade at will just by snapping his fingers and can now transform them to their unique forms.
second phase: after dealing enough damage, Nomura his impresses by your strength, only to say he was just getting warmed up and snaps his fingers again,. this time summoning about a dozen keyblades that surround him (much like Noctis and his weapons). this is where things get little tricky as he can now use combo transformations with his keyblades and with about dozen keyblades, there are a lot of combos.
final form: if you manage to survive and best the second phase, Nomura will commend you for getting this far, but says this is were he gets serious (as if the second phase wasn't hard enough). here, he motions all twelve keyblades and has them stab himself, enveloping him in a sphere of light. the light disappears and in its place is Nomura in his own keyblade armor (imagine a combination of No Heart and Eraqus' armor). Nomura now goes on the offensive and hits you with everything he's got. this is more about surviving than beating him. eventually he'll trigger a Situational Command in which you can counter his attacks and send it right back at him.
if by some remote chance you manage to survive the third phase, Nomura changes back to normal, congratulating Sora for actually beating him, and comments that it has given him inspiration for the next saga. Casually, he walks away but not before giving Sora a new keychain and tells him that he looks forward for a rematch next time.