True but then SEGA would have placed the game with another one of it's development studios. There's also the possibility of a hack 'n' slash game, which I believe is more likely than your suggestion, however still unlikely. There wouldn't be much point in getting the WHFB license for a hack 'n' slash when they could have just gone down the Spartan/Viking route again and saved some cash and increased profit margins as in this day and age I don't see a hack 'n' slash selling brilliantly even with a license (see LOTR: War in the North last year).
I think it's fairly likely it'll be an RTS, perhaps under the total war brand, perhaps not. With massive monsters and magic and uberstrong heroes that can munch their way through rank and file, it'll have a distinctly different feel to RTWII. Considering it's only just been announced now it probably won't be released until late 2014 putting a whole year between it and RTWII. So even economically it wouldn't be too affected by being an RTS also.