I fixed the RNDIS default config on Sailfish OS and got most of what I wanted outside of this. It's still a really cool project and I really hope at some point we'll manage to get it to do what I wanted it to do.

But now if I connect my Sailfish phone directly to a computer it will create an out-of-band network between it and the computer, enabling me to have the computer communicate with, oh, say, the software running in a LXC container on the phone.