Federer at Wimbledon (hopefully winning it one last time). That's his true home. He shot to fame as a Wimbledon champion and it would be poetic if he ends as one.
Anyone with me?
I don't think so. For me Wimbledon is still synonymous with Sampras, more than Federer (and Sampras' last match there was on Court 2 - what a fail by the organizers!). Winning it again won't be easy as I think Murray/Nadal will be back in the hunt. And I also think he'd want to play Basel at least one more time the year he retires, so Wimbledon wouldn't be the last tournament.
Nalbandian will definitely be in Argentina or a DC tie. He's not done well enough at any particular tournament often enough to have ties to it.
Nadal at Wimbledon is actually conceivable. He'll limit himself more to grass and clay in the future anyway and will be less competitive on hardcourt quicker than on natural surfaces. May go for a final clay court season and then grass, which he loves, and bow out on Centre Court - the scene of his greatest triumph. Actually can see that appealing to him, rather than trying to play Rogers Cup and the US Open etc. at the end with battered knees. Hope for Rio 2016 or Wimbledon 2017.