It is a much more expensive proposition for supersonic cruise engines than subsonic so even more critical you get an engine OEM onboard, figure out your market, and get a solid design point nailed down quickly. If you're off even a little bit in efficiency, it will very significantly affect the aircraft's market viability. If I were an engine company, I wouldn't put my own R&D funds into this area yet, and especially not toward Boom's design point.
Even more stupid things than Boom: commercial endoatmospheric hypersonics, and SpinLaunch. I can't believe SpinLaunch has funding.
The one "science fiction becomes reality" concept that could one day (not today) be viable is sub-orbital (exoatmospheric) point-to-point transport. But there's a long way to go to make that more routine and it's hard to see a path to safety better than subsonics. Subsonic/transonic commercial transport is a real sweet spot.
Claimer: I'm a practicing aerospace engineer, and do not work for Boom or their competitors.