Having bus functionality enabled in kernel is beneficial for several reasons. It strips out lots of unnecessary bells and whistles and just hold some skeleton for send/receive/advertise. Most POSIX IPCs don't have an advertisement mechanism that enables discovery without some external persuasion.

D-Bus does this but has often been criticised for being overtly complex. OpenWRT came with a simpler solution, but then quickly defined a data protocol which suffers severely in I/O - it needs JSON for everything.

BUS1 doesn't specify a protocol for actual data itself so I can send/recv C struct which my process groups know about it.

Also, leaving bus logic in kernel would mean I can write a minimalistic library wrapping the syscalls for my specialised use, yet keep the applications readily portable should plans change.