This is a terrible prediction. This project is extremely easy in comparison to California HSR because it’s all running in the I-15 right-of-way. There’s also no reason whatsoever to think you can’t run high speed trains on this route.
I don't think the commenter meant this route was especially unfeasible. I think they were referring to the fact that the track record (no pun intended) of high speed rail projects in the U.S. is mixed to terrible.