I was really happy to see that blue spec was fully open sourced in recent years. Does anyone have experience with a non trivial project with it? Does it have any traction anymore in real silicon development.

Same here, looking for an excuse to use it. It takes some time to get oriented. The BSV fronted makes it easier though. Have been dabbling in it as a hobby on the side.

While there have been tape-outs by universities, I think the learning curve would discourage traditional hardware companies focused on TTM. While bluespec has higher level abstractions, it also provides access to low level HW optimization features like multiple/gated clocks, integrate verilog etc. so I don't see any hindrances.

One needs to be familiar with both using SW abstractions and HW design, which iss a small subset that limits it's usage.