For a human controlled safety car I dont think it needs a special car, lights on top would be nice but all it really needs is a special skin. An AI safety car would be good, provided it was deployed and called in by admin command. It doesnt matter that the AI cannot drive well, it's purpose is simply to pootle about and not drive into whatever accident is on track. The drivers do the rest (and usually this appears to be driving into each other at low speed)
It's really something that will only ever be seen in leagues, and at the moment leagues that do this use a Human being - the disadvantage i've had in the past is that it has meant that I have had difficulty typing race control messages whilst driving the safety car, so now we have two admins for race day.