This is what my friend just accomplished.
This is what happens when you merge ArmA II files into ArmA III.
Expansions
(http://cloud-2.steampowered.com/ugc/702853606486331028/2CF7FA8BA927DB7918E0EB063D572B36FB9FB62B/)
Chernarus on Editor
(http://cloud-3.steampowered.com/ugc/702853606487229060/6069AB2CC4B90D3B98A246CD120086D6339D4EA2/)
In Chernarus
(http://cloud-2.steampowered.com/ugc/702853606487509980/AC5391AACDD57CC87423EFD873A25BDCD1BB1D3D/)
He can play singleplayer campaign perfectly with some animation bugs, just not multiplayer.