I’ve just written a tool to allow multiple clients to write to the FvwmCommandS socket without worrying about locking. I’ve used it specifically to allow me to communicate with FvwmScripts. I have also included two FvwmScripts and the clients that communicate via the multiplexer to supply them with data. One client/FvwmScript is an xmms2 client and the other is a HellaNZB status tool.
You can find out more and download the various bits at:
http://alex.foxybanana.com/fvwmscriptmux.html
Sounds pretty nifty, I might have to play with this some more when I finally get around to rewriting FvwmMpd. I don’t think the things you list as drawbacks are that much of a problem, expect for the script path, that’s sounds pretty annoying, afaik that’s one of the arguments FVWM passes to every script it calls (been some time since I messed with that though, so I might be wrong)
I can actually call the Module FvwmScript from the ``Muxxers,‘’ so when I get around to it, the entire loading process will be handled internally, without any expicit pathes or any of that. I’m just kind of busy because I’m participating in the Summer of Code and so really shouldn’t be off writing other code 
I’ve made some updates to the Muxxers, which one can find here: git.geekfire.com/?p=FvwmScriptMu … ;a=summary In general all development will be done in this git repository. I will hopefully be porting xmms2Mux to chalyx which will allow it to work with with MPD as well.
Alex