It has been arguably very succesful for prosumers, but it doesn't have the feature set required for a truely pro level wildlife body. given the choice, I would gladly take a 1D4 over a 7D
And herein lies the problem with the 7D:
It's not a true pro camera that appeals to pros and commands a higher price.
At the same time, it's a bit pricey for consumers, compared to the very competent D7000, for example.
So, the 7D market right now is mostly consumers willing to pay a premium.
This market is limited, though, and if Canon had a D7000-equivalent, it would all but disappear.
This is exactly what happened with the D300s market after Nikon released the D7000.
Looking forward, Canon either needs to make the 7DII a true pro body or move the 7DII downmarket.
These days all pro cameras are FF, so making the 7DII a true pro body means making it a FF camera.
If this happens, it's unlikely that the 7D moniker will be kept, though.
And if moved downmarket, the 7DII won't be called 7D either, since the next level down is the xxD series.
So, there you have it.
The 7DII will either be a FF camera (unlikely) or it won't be called the 7DII but the 70D.