I'm willing to put development effort into MIDI and sequencer support for FreeBSD. I will connect with the multimedia mailing list but I'm also interested in experiences and efforts that people from this forum have done.
FreeBSD currently supports jack, and end-user applications concerned, jack is the only MIDI transport system that actually works. The entirety of MIDI IO is performed by jack, while physical USB devices can be connected through only FreeBSD native facility that's actually usable in 2021, the umidi driver.
For end-user applications this means the "DAW" stack is missing the control protocol in the protocol suite. In order to connect the entire stack one must target jack API and leave OSS behind.
For instance, I've come to conclusion that for my workload, it's better to look at classic abandonware 16-bit PC applications, such as Voyetra Sequencer Gold. These applications were standard of the day, they have quite in features, professional documentation and keyboard driven. Stupid as it sounds, a SVGA application scaled up to desktop size might look better than some Linux toolkit UI program that didn't pay attention to DPI and things like that.
Right now I am looking to patch dosbox-staging to connect emulated MIDI to jack.
Although this will give me the functionality I seek I find it quite stupid FreeBSD doesn't have a native OSS compatible MIDI facility (but elaborate and controllable with virtual device support and routing) and I'd rather concentrate my efforts in patching jack to use FreeBSD MIDI than patching dosbox to use jack because I only care about FreeBSD on the project level.