I thought there where also quite some development in zynaddsubfx/zynfusion regarding midi learn and stuff.
I prefer Yoshimi over ZynAddSubFx, for several reasons, midi learn usability, GUI, performance, etc.
Carla single should be able to run a LV2 plugin as JACK standalone application (more or less I guess, it's still a plugin I would think). That's why it would be nice if it would support NSM.
Yes, I've tried Carla, it's nice, but I stick to use standalone programs,
open it using scripts, and connect them using aj-snapshotI know there are a lot of things that I cannot do with scripts (audio file managment, undos, etc etc) but now I will keep with my current setup.
Non-session-manager with jackpatch (saving your jack connections)
and maybe nsm-proxy if you need it, could be handy to manage such
a sessions of course. But stick to what works for you. Again, good
luck and have fun.