I think support groups are a great idea, especially for part-timers: it's easy to feel disconnected from PhD life. I've never encountered a PhD student support group. I'm a part-time student and live 2 hours away from my department so I feel te lack of this particularly strongly.
I think it'd be a good idea to start something, even if it's just meeting in a coffee shop every now and again. What to people think? I live in the Northwest.