Awesome reference to Excalibur. I think there are probably a surprising number of other "long tail" attempts at better BBS graphics.

One I used as a kid was OMNI BBS (sometimes written O-M-N-I BBS) which ran on windows: http://www.bbsdocumentary.com/software/IBM/WINDOWS/OMNIBBS/

Only a few of my friends ever dialed in but it was a next generation replacement to a custom qbasic bbs that I had written.

The OMNI BBS admin interface seemed to borrow heavily from Visual Basic and even included Basic scripting features so that you could program entire games and experiences. Unfortunately it was very buggy and combined with my amateur coding skills I didn't get very far with anything beyond the basic built-in features of email, message board and file repository.