I planted some NWSG three years ago. It was just a test to see what it would do. It is just starting to become visible this summer. The end of last summer you could make out a few seed heads and I could identify a few of the larger plants. I planted big blue, little blue, indian grass, switch grass, eastern gamma - I think that was it. The areas that had established fescue very little came in. The best area I have was a wooded area that I cleared. I planted that and then grazed it early the first two springs to get the cool season grasses and weeds down and then let it set the first two summers. It came in really nice, but it is almost a pure stand of NWSG, not much of anything else in there. There were a few bare areas in the middle of my fescue that some came in. I guess we will see what it looks like in 6 years. I hope it doesn't go back to straight fescue like Dun says.
I planted bermuda grass about 5 years ago - I haven't seen any of that either. I don't know if I am too far north and it all winter killed, but that was a complete waste for me.
I did plant alfalfa about 5 years ago in most of my fields and it is still going strong with the fescue. It seems to do really well. Besides the NWSG, it is about the only thing I have in most of those fields that keeps growing in the summer heat.
Like everyone else has said, NWSG is different to manage. If you don't rotational graze, I wouldn't even mess with it. It will not take continuous grazing pressure, even if it is established - or at least that is what I have been told and read.
A few things I would NOT do if you do try it. Don't fertilize - the fescue (and weeds) will go crazy and the NWSG won't. Don't lime - most NWSG does better at a PH of high 5 or 6. Fescue likes it a bit higher - if you have a PH in that 5.6 range, the fescue will be stunted and the NWSG will do well.