Unfortunately to participate in Audiobus an app *must* run an audio engine and adding a dummy audio engine to MidiBridge would affect its performance, so I'm sorry this is unlikely to happen with the current state of play.
Not only did I have thoughts, but around October last year I had discussions with Michael and Sebastian to convince them to cater for non-audio music apps (eg. MidiBridge, Genome, Little MIDI) as well as merge/migrate the OMAC/Audiobus app registries. I'm afraid I was not successful on either front. Maybe this will change in the future.