Starlink seems like a no-brainer at this late date, but I remember thinking "He'll never be able to make money from internet satellites. This has to be some kind of scam. Look what happened to Irridium."

Data centers in orbit certainly seem like a pipe dream, but SpaceX certainly has the technology it needs to put them there, and that's a huge competitive advantage (like it was for Starlink) if they do turn out to be feasible.