I'm betting that it is a new class of ships. The reason moms got renamed to super carriers was so CCP could release a new type of ship somewhere down the line. Although most players still consider moms and SC's synonymous, the devs have been more careful to call them SC's.
It seems likely that if the sansha 'mothership' mentioned in the interview was, in fact, a SC, that someone would have corrected it in the press release and the incursion web page. Since they have been throwing the term mothership around a lot, it can be reasonably inferred that they mean mothership and not SC.
If you look into lore a bit, i believe there were jovian motherships that served a logistics purpose. Id put my money on the new mom being the logistics boat that the old SC's wanted to be. Something with the tank of a titan, and the repping power of a handful of carriers. And some fighters/bombers for offensive purposes, but not enough to make it offensively superior to a SC.