I don't know much about it, but I think it is the next step in the evolution of MIDI - a way for digital instruments and controllers and computers/software to talk to each other, but through a firewire-type hook up which will, I imagine, increase performance and ability (in what ways, I do not know!)
Besides Yamaha (who invented the technology) I know Korg made the Triton-Rack mLan capable. As far as every other manufacturers jumping on the bandwagon, I don't know.
It will probably evolve the way MIDI did - lots of manufacturers will probably make mLan compatible gear, and the technology will grow into the gear, if you know what I mean - the way MIDI did. I am sure MIDI does more now than the inventors thought it would - or maybe they had an idea that they knew others would run wild with.
Brad