IIRC Corpse was working on such a map years ago, with FO1 maps and new ones all added in.
Unfortunitly he's too anal about having sixty bajillion guns with realworld sounds for each one.
TBH Im suprises that so far noone has simply re-made the maps themselves for FO2.
Junktown would be easiest, 95% or more of it simply could have changed in the 80years since.
Shady sands is allready in of course, ditto V15, would just need to re-ad the 'back' door to it that the player used in FO1 (unless thats what the squatters shack entrence that was unusable was)
V13 allready in it.
The Cathedral would be easy, big ass crater.
Military base allready used as well.
The Hub/LA would be a bit of a challenge, you'd have to rebuild the towns AND add more onto them while making changes here and there to the pre-existing parts (cause some buildings would have burnt down or been replaced in the time since, infact a lot might have been replaced due to the prosperity they've had). LA, you'd have to rebuild AND update quite a bit.
BOS bunker interior would be easy, wouldnt have changed too much. Surface would have to have a town on it, a main town area, then outlying farms (because it would both make sense and add to their prefernce to be isolated to allow farmers that want to be left alone to settle there in return for protection and being well supplied in return for the food they provide, prehaps a small scale manufacturing center of various types as well. One for ammo, both re-using brass as well as making new brass and rounds+powder, and another for making weapons, plus it would allow the senior scribers to concentrate on the hi-tech stuff while the junior ones gain experince making lowertech and weaker weapons to flood the market with in return for lotsa gold and supplies for the BOS)
Necropolis would be a pain cause it has so many buildings, and would also have to be updated to have some limited industry, plus the vault repaired a bit. Prehaps a building or two in a 'smooth skin' district with regular human merchants and what not.