I created an entry in the community wishlist requesting the *arcade* versions of Mortal Kombat (mk1, mk2, mk3, umk3, mk4) to be available here on GOG. Anyone that is interested is welcome to vote and to add comments: This entry can also be found manually in the community wishlist by entering "arcade versions of mortal kombat" in the search box there (in the games tab). Entering mk1 is easier and should also work.

I guess what you are asking is the emulated roms of those games, kind of like SNK does, where most of their games being sold are just ROMs running in some emulators. I would bet is not a decision GoG can make, and is the publisher who needs to decide to publish their games that way.

Personally, I prefer GoG to stick to real PC games, rather than selling roms, but is just a personal opinion. I'm sure some people do feel bad about getting roms illegally and running them in your emulator of choice, me? not really.