Your correct, I think its up to SE to take the ideas we give though if they chose to use them at all. I'll copy your comments into the OP.
I used the Ninjtisu Meta Magic idea as a way to allow the Vagrant to have an AOE casting ability while preventing it from being used for a specific spell type. Ninjitsu normally cant be casted as a AOE spell so using Ninjitsu to modify the source spell and restrict it from AOE allows the Vagrant to still have AOE casting for other non-ninjitsu spells he learns like En-Elemental.