You can do this actually, to a point. If the base models came from the same source -- and so all the objects had the same GUIDs -- you could do this with the XMI import/export or something similar. But it isn't smart enough to try resolving objects by name / path.
It isn't an explicit use case we are addressing right now though, and problems could arise if the two base models had differences in package structure or if classes were deleted. We will start adding support and tutorials for this moving forward though, as it is a good way to share profiles.