I was always under the impression that WoW was essentially a cockblock for another Warcraft RTS. As long as it was 10m+ subs strong, it probably wouldn't have been a logical move to break your team up for an RTS.
I enjoyed Warcraft off and on for years, but I prefer the RTS game. I'm hoping that over the next few years when WoW levels out around 1-2 million subs it will allow Blizzard to move some people onto Warcraft 4. Predicting WC4 2016