It kind of depends on future sensors. If I was to use a NEX 5n, I'd be happy to use almost any legacy lens, whether Contax G, Leica M, Voigtlander or Zeiss M. I'd probably go for a Leica only set-up. The NEX-7 sensor excludes symmetrical lens designs, so I would run into trouble with older lenses wider than 35mm and with modern Leica M lens prices being what they are ...
I'm quite attracted to Contax (SLR) lenses and think the 18mm, 35mm, 60 macro, 85mm and 135mm lenses would give very good service.
I hope to be able to team up a set of modern Zeiss E lenses with a NEX-7, so here's in hope: the existing Zeiss 24mm, plus (hopefully) future: Zeiss 14mm, 60mm, 90mm and 135mm.