Sorry but, to me, this has disaster written all over it.
I think it has success written all over it, as much as any series concept I've seen for 2013-14. There's all sorts of less likely stuff. People trapped living under a dome? A kid who finds out he's the descendent of ancient Greek gods? The adventures of Huck Finn and Tom Sawyer in Steampunk New Orleans? S.H.I.E.L.D.
is one of the few series concepts I'd be willing to bet money on succeeding. Everything else is either derivative or nutty.
Setting it after The Avengers
movie is really the only option. Anything else would confuse the audience. You can't expect them to pay close attention to when it's set, etc. They're viewers, not fans.