At least from what other radio telescopes, the issue isn't actually the physical satellites. It's the spectrum they're using

>no real benefit to doing that over launching a single large telescope in terms of launch cost

It would be hugely beneficial to do it in space. When you do interferometry on the ground, your maximum aperture size is the diameter of the Earth (if you had two observatories at opposite points on the Earth). When you do it in space, the size of your synthetic aperture is practically limitless.