... I get what you're saying, but I think the Unreal Engine is going to continue to be a cash cow for a good while yet.
Another data point: id was killing it (and, to us, Carmack remains undisputed). But they completely lost out the next generation, to Unreal, because of vehicles. I don't think that'll happen here, just disclaimin' past performance is no guarantee of future success.
Though, to be fair, the Quake engine underlied Call of Duty, the most successful franchise (I believe), and it really showed in the framerate. Note: no vehicles. And yes, past tense.
It has nothing to do with vehicles.
Re: vehicles. I'm going by what Carmack said in an interview.
He was talking aboout the time around Unreal Tournament 2004, and at that generation, it was a big thing (kinda like waving grass was at one time).
Sorry, I don't recall which interview (and it would be hard to google unless there's a transcript). It might have been one of his keynotes, perhaps the one with Rage on an iPhone. I'm pretty sure it was a long one (at least 1.5 hours). It was one of the big popular videos on HN/r/programming (not an esoteric one).
Note how many games have come out using UE3, think about the royalties coming in.
Also, right now they have just about the best game-engine, only hobbyists and some indies would choose Unity, mostly because its easier.
UE4 will definitely get several high profile games soon from big AAA companies.
I would say that Unity is in deep trouble right now :P