From what I remember, the problem is that there is a fairly large amount of work to get useful performance out of a hybrid like that. It's easier to just, say, learn CUDA and use a GPU than it is to have HDL folks work with SW. I have no doubt a system like that would be useful, but it would probably be expensive and limited to specialized, low-volume applications(like big FPGAs are now).
https://www.nextplatform.com/2018/05/24/a-peek-inside-that-i...
From what I remember, the problem is that there is a fairly large amount of work to get useful performance out of a hybrid like that. It's easier to just, say, learn CUDA and use a GPU than it is to have HDL folks work with SW. I have no doubt a system like that would be useful, but it would probably be expensive and limited to specialized, low-volume applications(like big FPGAs are now).