Im comming from ruby and golang and i am really liking rust so far. Its more verbose and complex to program, but also, much faster, rewarding and safe.
In golang i dont think rack could be so relevant as in ruby because of the stdlib, but in rust, like ruby, we dont have a mux or http server in the stdlib, so, in my opinion we are going the same way as ruby in the early days. Some people doing web frameworks, others doing web servers and a hell to put all together.
I really like the fact in ruby that you can program a sinatra app and embbed into rails, the middlewares work in almost all frameworks, because in fact, they are built for rack and every framework implements rack.