It might be an idea to choose and designate an area as a sort of, city akin to the spawn village in the last server. Getting a place where people specifically are meant to build together, might help to promote some more activity if not a lot of people are playing. Not that I'm of course one to talk, as I've not been on very often (been playing FO:NV) and even were I to play I'd probably work foremost on my own base which'll still take me forever.
But if people had a place to build together, maybe with the only restriction being to mark out one's plot ahead of time with some gravel square or whatnot, perhaps with restrictions on size and with some small consideration to roads, then might get more people on, for a time. And it would be interesting to see how the city developed organically. Not sure what place would be ideal, aside from that desert with the portal place though building in a desert is sorta crappy and I'm not sure what houses are nearby that may eventually get infringed upon.