There's probably a lot of technical hurdles just to making a whole new type of engine. But they also need to design and build a new space plane. That's a brand new supersonic airframe.
There's a lot of engineering needed here. I hope we can see some indication of progress soon.
If they manage to get enough speed from the air-breathing phase, they may even have a single-stage-to-orbit + VTOL vehicle. Now that's a seriously cool tech to have.
The reason we do aerobraking and parachutes is that our engines are not efficient enough and we can't carry enough propellant to decelerate to a landing but if we have engines efficient enough, we can have a single stage drop a payload close enough to LEO that a cheap second stage can finish the job and the booster can still do a powered landing after circling the planet once, we have a game changer.