Until someone can figure out how to increase the efficiency of a propeller traveling at near supersonic speed, you will not see an efficient turboprop that can go Mach .80. And until someone figures that out, RJ's will continue to dominate the market.

Does anyone know much about the TU-95 Bear? This bomber could go as fast as a B-52 and it used 4 turboprop engines. Was it just incredibly inefficient, or did they develope something to solve the problems that keep propeller aircraft slow?