You cannot export to M3 with Blender that is unless your purpose is to take/steal from SC2 for some other game. Usually the rules state that models between Blizzard games are allowed, not outisde of them. I'm using some portable version of 3ds Max Design 2011 x64 as a tool for import/export m3 with having the M3 script, so far it works nicely, not even slight implication for a tool similar to Magos model editor is coming for sc2..