Can't see that working very well since they're single-user machines with little to no facilities for time-sharing (and part of the endearment with public access systems is getting to time-share them like they were supposed to and all). If you're doing emulation anyway, an alternative could be something like "ssh in with X forwarding and we spawn a dedicated lispm, connected to a chaosnet network with other emulators and all" (if you're feeling fancy maybe throw in other public systems (ITS?), or let people connect bridge their own stuff in or whatever), which would be kind of like using a lispm in an actual lab, but I don't know how cool that'd be.