Impossible to know without knowing _why_ it works. It's in contradiction with what we currently know of physics (so it's still far, far more likely that NASA eliminates a few more possible outside causes of the tiny measured thrust and the effect disappears), but if it does work then who knows what else could also work.
Actually, there are several in-universe articles saying otherwise:
The interaction between the shields and a conventional propulsive system would be horrible (you’d get fried in your own plasma).
Therefore the Interacting Magnetic Pulse system (sorry, I’m translating back here, so I dunno if that’s the correct term in the correct in-universe article in english) actually uses some weird interaction of microwaves to create "gravitational waves on which the ship then rides", as one engineer said poetically.
It would give us one more point of serious divergence between our physics theories and the real world. What would that give us ? Good question.
Something between what the discovery of the bandgap in semiconductors got us and what finding out that the speed of sound in cheddar cheese is much more temperature dependent than in brie.
CHEMISTRY: Antonio Mulet, José Javier Benedito and José Bon of the University of Valencia, Spain, and Carmen Rosselló of the University of Illes Balears, in Palma de Mallorca, Spain, for their study "Ultrasonic Velocity in Cheddar Cheese as Affected by Temperature."
REFERENCE: "Ultrasonic Velocity in Cheddar Cheese as Affected by Temperature," Antonio Mulet, José Javier Benedito, José Bon, and Carmen Rosselló, Journal of Food Science, vol. 64, no. 6, 1999, pp. 1038-41.
WHO ATTENDED THE IG NOBEL PRIZE CEREMONY: The winners delivered their acceptance speech via video recording.
In an unpublished NASA report they are seeing over 100uN when feeding 80W power to the drive. Assuming a spacecraft to weigh a ton, that would accelerate it by ~3 m/s per year. So it's not only a question of EmDrive working, but also a question of whether it's possible to scale up the technology.
Isn't that an incredibly tempting figure? Almost like the result was picked because it almost has to be commercialized?
You'll get various war stories about what it really took in practice for satellite XYZ, but geosynch satellites burn along the lines of fifty or so m/s of delta-v per year for station keeping. To a first order simplification its true that you launch a geosynch comsat into space and it stays over the same general point on the earth for infinite time, blah blah but in practice there is always slow drift and impact of solar winds and lunar gravitation and whatever, so its not actually motionless and requires continuous, eternal, fine tuning.
Anyway using a couple hundred watts to completely eliminate the stationkeeping thruster fuel completely seems a fair enough trade...
And yes I know stationkeeping isn't a perfect continuous demand for thrust all year long, etc. Still, its interesting, and of the right magnitude, more or less.
I don't think it would be terribly useful for human transport, true. But its suspiciously right at the mass, power, and thrust values required to be commercially viable for comsat station keeping. That's either incredibly lucky, sometimes the universe does smile on us, or ...
If it works, it would mean that you could go into space without reaction mass. It would open up the possibility of relativistic travel. You could build a rocket the mass of a VW camper and push it into space by remotely powering it with lasers, as all the EMDrive apparently needs is electrical energy.