Several schemes have been proposed to provide actual "transit" service on parts of the old Placerville line using large speeders. None have ever emerged from the pot adequately cooked, other than occasional excursion runs on part of the line that's in the country with only one grade crossing (and even that can be avoided for most runs). Suspect that the city and/or JPA insisted on substantial insurance even for the occasional stuff. And providing regular service with speeders, even big ones with enclosure, just doesn't fly under present-day laws and liability requirements. Tough luck.

I can see the speeder and rail-bike people getting permission (with some insurance and other standard safety requirements, and maybe a little maintenance work as in-kind payment) to use the line for non-revenue trips while there's no regular rail service. That seems likely to be the case for a while yet, except for SCBG's runs to the Boardwalk.