Supersonic Roller Coaster-cum-Aircraft patented by an Airbus Group Company
I don't know which is more of a pipe dream: this thing or Fireball XL5. They managed to combine live action and CAD in this video, but the technology to actually build this thing is still decades away. Still, it's nice that people are turning their dreams into digital models.
Boeing and a group in Australia have been working on a hypersonic ramjet.