Deej didn't confirm anything. Until he says "There is only one explorable zone per planet" I think we are all interpreting this our own way. Personally I just though he meant four destinations (Earth. Moon, Venus, and Mars) but there could be multiple locations. I mean why would they make concept art for so many locations and then only have Russia. The concept art included Old Chicago, Mumbai, European Dead/Flood zone, and the Twilight Gap.
HERE IS THE KICKER
This is a link to the mars map tour where a 2:26 they said they work with the people who work on SP to derive from to get the art design for MP.
SO this second one shows a map from the twilight gap, which an area that can be seen from the last city and is definitely not Old Russia. You get small glimpses at 9 and 12 seconds.
Why would they have multiplayer maps that aren't derived from SP art styles if he said the maps do exactly that? People need to use their brains.