I’m not saying it’s done widely, but it’s possible. The implementations I’ve seen are not ready for large scale primetime, but if you’re just hosting a BBS, how would it be different than an old dialup terminal?
Vulnerability is dependent on the implementation, not just on the naute of the service. There is nmore than one implementation of “telnet on port 23.” I’m sure the one that I got hosed through is easily hit with buffer overflow leading to automatic root access. That’s what was done to me. Other implementations may be more secure.
I spend time on irc, daily (near full time) and on other people’s hardware, so that works for chat like activity. A bunch of freepers did that for the Iraq war and for the Bush/Gore election fetivities.