Lots of theories, but I never came across anyone that claimed to have made it work. Your main problem sharing devices on a bus on a keyboard is that they aren’t designed to actively shunt data around at the same time, so you risk corrupted data if any one device interrupts the other. Computers’ OS’s are designed to do this but keyboards rarely have full bus sharing routines built in.

I think the Roland dongle was really designed for other gear and Roland just tried marketing it at the BK user without thinking about the ramifications...