off topic, but could help still: i was searching mkvsdcu files,starting with coalesced ini,i noticed that it says player downloadcontent id: shaokahn=1000 and below it darkseid=1001.
and above this you can find player and IsMK for mk chars and IsDC for dcu chars(example:IsMK=scorpion)
maybe if we put darkkahn=1002 and the remaining stuff(adding his vs picture etc) we could get him playable and another npc who also has the char prefix like darkkahn,char basemale medium.
and mkvsdcu is referred thorough the game files as mk8.
interesting stuff,because shao kahn and darkseid are on a extra menu,and with this references that indicates that it is the game's dlc chars menu.
mk8 or mkvsdcu even has an arena section where the arenas that support test your might or freefall are listed.
hmm all this resembles mk9 doesnt it?
just posting some stuff i found.
EDIT:mk9 tweakvars has references in mktweakvars to various xxx files like npc classic jade,but also other strange things like Toasty.