I was going to write quite a detailed answer to this question but Lenders has pretty much said exactly what I think.
Original thread topic.
He's in the mix of course and will always be. The main effect of his age though is that his recovery powers have greatly diminished, grueling matches affect him far more in the next round than his younger rivals. To maximize his chances, he needs to get to the semis fresh; this means avoiding Tsonga/Berdych/Delpo in the quarters either by drawing Ferrer/Tipsy or by having them lose early (which is entirely possible). It's not that he can't beat those 3, but he'll almost surely have a battle on his hands and then come out flat in the next match like this year at AO (flat performance vs Murray after long match with Tsonga).
If he can get himself to the semis as fresh as possible, he's always got a chance. He'll still want to avoid Nadal (although we still don't know in what form Nadal will be in upon his return), but he can beat anyone else. The problem is AO and USO are played on super slow hardcourts and are extremely physical Slams, as is Roland Garros. Wimbledon (especially if the roof closes) seems like his best chance and it is if he gets to the semis, but it's also where he's more likely to get blown off the court before semis. I will never discount Federer, but it's going to be tough; this is the most physical era of tennis ever and Federer is way past his physical prime; he's still way superior to most of the field though, which he will need to rely on to get to the semis without as little as fuss as possible so he can stand a better fighting chance against the moving walls in the top 4 who will get everything back and really test him physically.
No outcome would surprise me here, it's just very unpredictable how Federer's career will unfold from now on. No more Slams, one more or a few more are all possibilities. Of course he needs to schedule his year smartly, but he always does that so it goes without saying.
As a fan of his, of course I would like to see him win more Slams but I have to be realistic. I thought he would get to 16 so I was delighted when he won AO 2010. Everything after that (including his 5th and 6th WTF wins, his 7th Wimbledon win and return to #1) have just been icing on the cake.
Take the most recent AO for example. Sure he lost in the semis, but the way he went down fighting made me proud to be a fan. We have to accept that he is no longer the favourite for Slams but as long as he plays like he is, he seems set to be in the group of likely contenders for a while to come.