Speaking from a sports shooter only:
The frustrating thing about the 7D is that Canon said it was for sports shooters and...The 7D pretty much sucks at ISO 800 and higher. I would know because I tried to shoot in the trenches with it for indoor basketball and volleyball for 2 years with a 1D4 as the main camera. The 1D4 kicked it's a$$ but I needed the reach. I guess my standards were high but it was awful. Shooting to the right doesn't always work. If you're at f/2.8, or worse, f/2.2, 1/500s, and still at ISO 3200 or 6400, there's nothing you can do. You can shoot to the right or whatever you call it but the only option is to slow down your shutter speed and now you have blurry athletes. Since I pretty much always shoot indoor sports wide open or close to wide open (depending on lens f/2.2 or f/2.8 ) at 1/500s and EC +2/3EV with CWA or spot metering, this was a real pain with the 7D. It wasn't as bad with a 1D4 and not nearly as good as FF.
When you went to FF, all of the problems were solved. That's what was so great. We could blow up action shots at ISO 6400 for the universities and print them, no problem. The 7D replacement really needs an improved sensor. In the collegiate scene I rarely see any cropped cameras anymore; it's all 1D4 (cropped), 5D3, and 1Dx. In fact, I did all three each of the D1, D2, D3 NCAA Track Meets this year and it was unusual in that most shooters had either a 5D3 or 1Dx. In years past that wasn't true as I saw plenty of 50D's, 7D's, 1D4's. Oddly, not this year.
Mirrorless will really have to improve to appeal to action shooters too. The AF is so erratic and slow it's just well, plain awful. I think the concept has potential though for other things. Just not for me.
Due to all of this, I will be watching the 7D's replacement very anxiously to see how it performs. If it performs decently with a better AF system, I will buy one and use it outdoors, for sure. I still don't think (my opinion) that it's going to match FF though.
On the other hand, I agree with the frustrations FF brings, meaning now you need longer lenses and a more expensive camera. It can be quite cost prohibitive.