RE: Radeon Pro WX 4130 with 2GB GDDR5 card for Dell Laptops?
MXM-A is not completely different but the cards are appreciably smaller. Try wikipedia - it has the specs.
The default answer on compatibility is no - the BIOS in the system isn't written to recognize the new cards. It may or may not be possible to get one to work - but the system isn't designed for the new cards -- and short of trying (or finding someone who can demonstrate having done so), it's a trial and error exercise.
Since the M4600 won't even take all the video cards from the later M6700 and M6800 systems, I think the answer to support is vastly more likely to be no than yes.