I just wanted to point out that thrust without expending mass is already possible without an emdrive.

Anything that asymmetrically radiates photons will generate a net acceleration. This very mechanism has been experimentally verified as the pioneer acceleration anomaly.

If the emdrive is some kind of special case of this mechanism, it's entirely compatible with existing physics. The proposals so far are based on mechanisms which are different, and incompatible with the existing understanding of the universe.

It's also worth noting that in 2016 the Chinese research team was unable to replicate their findings after accounting for a power cable that was magnetically inducing a force on the experimental apparatus.