Maybe it's time to run SchemeBBS using MIT Scheme 11.2.
It will take years for that to happen. SchemeBBS runs on the inferior FreeBSD operating system, where MIT Scheme has not been updated in more than 7 years. On FreeBSD, MIT Scheme is still stuck at version 9.2 (released in 2014) [1], while the rest of the sane world has already upgraded to version 10.1.x (2018) or version 11.2 (2021).
I don't know why people use the inferior BSD operating systems. On NetBSD, MIT Scheme is stuck at version 7.7.1 (released in 2003!) [2]. On OpenBSD, MIT Scheme is not available at all!
[1]: https://cgit.freebsd.org/ports/tree/lang/mit-scheme/distinfo?h=release/13.0.0
[2]: https://pkgsrc.se/branch=pkgsrc-2021Q3/lang/mit-scheme-bin