Scales with what Bruce? The reason it has too low a thrust is nothing to do with development, its to do with basic physics as Baez and others explain. You say that the ion drive "requires material to eject", of course it does, anything does. Because of conservation of momentum, anything which generates momentum in a forward direction must also shoot stuff out of the back so that the total momentum is conserved. Stuff can be matter, as it is in any conventional rocket and an ion drive. Or it can be radiation. Photons (including microwaves) carry momentum, and when I heard Shawyer talk about this about a decade ago, photons were carrying the reaction momentum. Photons have a momentum p=E/c, where E is the energy of a photon, and c is the speed of light. But as we know, c is a very big number.

I came away from Shawyer's talk not knowing whether the device wouldn't work at all, or whether it would work, but in order to get an emdrive rocket to take off you would need to put out enough microwaves to cook every living thing for hundreds of miles around.

Fortunately, having subsequently read Egan's and Baez's analyses, its the first.

Don't be fooled by Harold White of Eagleworks either, he has a paper which is claimed to be peer-reviewed, but who peer-reviewed it I don't know because others have subsequently pointed out large holes in the analysis. See here.