if this has come up before i do apologise ,it would be good ,if you could take the mudbox layers and export the them as Blendshapes directly into Maya ,possibly through the use of the FBX file format. just a thought.
All the best Robin

its already possible as long as it is the same subdivision level.  If it is a higher subdivision level, you would need to create some nodes to allow different displacement maps that blend with different blendshaps much like animated bump maps.

Yeah I know you can save the layer out as a blendshape ,which is what I do at the moment ,but it would be cool to sculpt a different Blendshape on different layers and Mudbox spit all of them over to a maya scene ,with all the layers as blendshapes

I tried MB to sculpt Blendshapes, too, and came back.  To Edit vertices, i really miss from Maya a wireframe or a Xray mode that allow me to move every VISIBLE vertice, even if there’s another part of the mesh in front of, for example to edit the corner of a mouth or an eye.
I also miss advanced tools to invert, blur and sharpen layer masks, in order to split shapes.