Check this:
If that's still a macOS limitation, then why don't you consider polling manually? How often do you need the polling to occur? This macOS command will list all paired BlueTooth devices:
system_profiler SPBluetoothDataType
Why not just issue that command every few seconds? That's what KM would have to do if macOS still doesn't issue events for new BlueTooth devices. I wouldn't want KM polling constantly if I don't really need that service.
I'm sure it wouldn't be too difficult to write a macro that polls the results of the above command every few seconds. (It's a very fast command. It probably wouldn't be a drain on your system's resources.)