I have a similar idea/desire. My thought/desire would be for something like this:
RRC-1258MkII at the radio site (FT1000MP)
PC instead of RRC-1258MkII at the remote sites. Some other software (Mike??) would be needed to "emulate" the RRC-1258MkII at each remote site. Maybe something like HamRadioDeluxe could be used as the "radio panel" at the remote site (it would take some work to get HRD tied into the RRC-1258MkII emulation software?). This would (in my simple mind) still allow each remote site to remotely use the rig (most important to me, I want remote straight key capabilities!). Since the PC is not at the radio site, the "hard to get to" location should still remain stable. Each remote site/user would need their own PC/software.
As for authentication, perhaps SSH could be used? Each user would send all of the traffic (audio, control, etc.) across the SSH tunnel. In this way, SSH would be used more for an authentication and transport mechanism (poor man's VPN) than for extra encryption. This would depend on the capabilities of the RRC-1258MkII to handle the extra work for SSH and maintaining a user database.
73,
-detrick
KI4STU