This does seem likely, but it won't necessarily be in this expansion. More likely than not it will be, but Blizzard also has a dire need to start sowing some seeds for future expansions so they can recycle less content. An N'Zoth raid would make a lot of sense in a future Azshara expansion (since we know we're not going to meet her this time).
If I were Blizz, I'd've tried to put out a Warcraft 4 RTS at the end of Lich King (during that massive year of work on Cataclysm after 3.3). Then they could have introduced a whole new range of lore as they did in WC3/TFT to follow up in Cataclysm and the next couple expansions.