Btw, I missed this message in the first place and in the meantime I created a python script using jackclient-python ( https://github.com/spatialaudio/jackclient-python/ ) to automate jack connections, since the only reason I needed nsm was to keep track of connections with jack clients that can become available or be closed at any time during a session.

This allows me to have a fixed "session", even when some jack clients listed in the setup are not available - using jackpatch I'd have to save a whole session with all clients connected and remember not to save it anymore.

Anyway, while your solution is the best for "closed" sessions, I still wander why there's no clean way to use OSC with nsm clients.
Unfortunally I only know about python, I can barely read C/C++, if not I'd suggest a patch that would allow nsm receive and relay messages to clients using the client's osc communication, something like /nsm/client/send; for example, with non-mixer it could be "/nsm/client/send Non-Mixer.aFOOB/strip/parameter/argument value" with nsm tracking down the client osc from the first part of the address. Anyway, this is just speculation at this moment, but it would be nice to see this implemented.