[DennisP]

I don't think anyone can say there are insurmountable obstacles, but it's still a hard problem they haven't solved yet. Bits of the rocket are still melting on reentry, and they have to fix that to achieve rapid reusability. Plus they haven't demonstrated a heavy payload yet. We can't be sure they'll actually achieve extreme low cost until they've done both of these things.

For anything beyond Earth orbit, they also need to demonstrate orbital refueling.

I've seen articles raising technical concerns about all of these, but I'm not enough of an expert myself to have an opinion.