I have a character complete with armature, and both the armature and the character’s mesh are linked from another master file - the OBJECT of the character and armature are not linked, but the MESHES are linked.
I can pose/animate the linked armature however I want, which is exactly what I expected, but all the Shape Keys on the mesh are greyed out so I cannot animate the Shape Keys! I was expecting to be able to animate the influence of the Shape Keys despite being on a linked mesh because by doing so, you are not creating any NEW mesh data, you are merely changing the influence of existing mesh data, in the same way that by animating a linked armature, you are not creating any NEW armature data, you are simply moving locations of existing armature data!
Also, some of the Shape Keys’ influences are driven by Drivers attached to bones (so when a leg bends, the muscle will deform accordingly), but these drivers are not working either, the the Shape Keys’ influence just stays as zero.
It would seem inefficient to have to unlink/fully append a character mesh simply to get the above to work properly, but is that the only way to have access to Shape Key controls?