PCExpress is already the PC's answer to /X (so far as I remember).
The really difficult thing is how much demand there is likely to be. Visiting a BBS is a great nostalgia trip, for sure, but there's no actual use for it.
Everything BBS's used to enable us to do, the internet now has a much better answer for.
Messaging = Email or forums.
File transfer = FTP.
Games = Take your pick!
Having said that, I'm setting up an /X BBS (slowly, I don't have spare time to dedicate to it - thanks to Minecraft). I'm planning on having an emulated Amiga environment for a telnettable connection, as I don't have funds spare to get my A1200 onto a network. The A1200 can have a real phoneline, as I've a spare USR Sportster modem.