I think they will release Sisters of Battle in plastic. There are just too many cool modeling possibilities not to. Not to mention leaving money on the table. There are many people, myself included, who would literally pelt them with money.
I do not think GW would combine Sisters with Grey Knights or Inquisition. Partially because they are separate and distinct entities but mostly because GW seems to like splitting things into separate sales. Like Cult Mechanicus and Skiitari. There's no real reason for their separation except additional sales for the codexes.
Also, I think we are more likely than ever to get new Sisters. GW is releasing things fast and furious. In order to do that, they're drawing heavily on previous work. The background and aesthetic for Sisters is already well developed so it's not difficult at all to expand on that.
And finally, GW seems a bit more willing to take risks. I wouldn't be at all surprised if we saw squats turn up again!
Side note: please, no references to clocks being reset. That meme has been overused, abused, and should be avoided.