I have implemented MusicXML import in csnd.CsoundFile. The MusicXML note data is translated as follows:
p1 Instrument number + 1 -> insno
p2 Time -> time
p3 Duration -> duration
p4 Pitch -> MIDI key
p5 Dynamics -> MIDI velocity
This could be used with the new extended score reader element in the CSD file by writing an executable script to load MusicXML and save it as a Csound score. I expect I will provide such a script in the Csound Windows installers example directory.