This is more that a single space-plane...
... The engine design is an enabling technology not that dissimilar to the original Jet engine (which the Brits also had a hand in).
- If you want to fly fast you need thin air. You can't do it down low. Too much heat from air friction.
- But if you want to fly where there's little or no air, you're going to have to bring your oxidiser with you. Which doubles the fuel weight
- Oh, and if you want to fly fast you need to carry a lot of fuel anyway.
This is why the Yanks were trying to build a hypersonic ramjet - it might go fast in thin air and still gulp enough air down to not have to carry oxidiser. But it doesn't look as if it'll be very practical, since it needs rocket launching.
A SABRE engine in a military vehicle could take off in jet mode from the good ol' US homeland, breathing air, then climb to a near vacuum and go hypersonic in rocket mode. Then, when it got to the target area it would descend, switch to jet, manoeveure and bomb the target. It would then return the way it had come.
I imagine that the US military are drooling as the possibilities become apparent....