Fenris447
Explorer
I wouldn't say it's impossible, but I think if WotC want their alternative race rules to be viewed as a core rules they wouldn't want to stick any setting related labels on it.
I can see them framing it as both. A Planescape theme can be tied into how diverse the multiverse is and therefore how diverse player characters can be. That would have the side effect of making Planescape an integral part of the core game, but I can live with that.