No rumours. Just mere speculation after reading this:
https://medium.com/swlh/macos-it-s-time-to-take-the-next-step-ee7871ccd3c7#.p3w3nk8ul
Although a name change does usually suggest a significant change of some sorts.
True, it usually does, but Apple is just phoning it home with OS X these days, so I'm not getting my hopes up for anything. Knowing Apple, they'll probably just add Siri and not much else.