Forget about calling it just Nintendo X. I can just see it now:
Kid asks for a Nintendo X.
Parent goes to store, asks for "games machine called X".
Parent goes home with an Xbox One, happy in the knowledge he has bought the kid what he asked for.
if the marketing is effective it won't be an issue
also I have a hard time believing a parent will go in asking for a "games machine called X" rather than "A NINTENDO" or "AN XBOX". and if they buy an xbox, the kid bitches and they go back and exchange it at the store for a nintendo