In an effort to save this thread from being further destroyed by more UCS Great Wall gibberish and other such things, I'm going to ramble off my thoughts on sets that are potentially up for retirement this year.
1) Tower Bridge - Being a late 2010 set, this one has already celebrated its fourth birthday, which is pretty old in Lego years. I could see this one going OOS in the fall and not coming back.
2) Pet Shop - 2011 set, the oldest active modular building. I think this one goes in and out of stock a number of times this year, ala the Grand Emporium, before selling out for good in the fall and being replaced by the next modular in January 2016.
3) Volkswagen T1 Camper Van - This one will be four years old in the fall but I wouldn't make any wagers on it. On the one hand, it has been out for a while and its successor (Mini Cooper) is already on shelves. On the other hand, it seems to be a hot seller (especially among the horde) and could easily last into next year, or beyond.
4) Sydney Opera House - I don't think this has been out for long enough to retire this year. I just don't see why Lego would pull the plug on it so soon -- I would imagine these big landmark sets are higher margin, lower volume items so even if the sales are a bit slow it's probably not unexpected.
5) Tower of Orthanc - This one turns two in July, so it's not very old. But it's a licensed set based on a soon-to-be-if-not-already irrelevant intellectual property. I think this one is gone for sure this year, and quite possibly in the next 4 months.
6) Palace Cinema - I've only included this in my list because it has been discussed a lot lately. Personally, I don't think a 2015 retirement for the cinema is even worth discussing but in the spirit of "anything can happen", I suppose there is a remote chance.
7) Ewok Village - Two years old this September. That's a pretty short lifespan, so I don't think it retires this year. But if I had to make a list of dark horse, surprise retirement candidates, this would be on it. Realistically, I think it goes in 2016 at the earliest or, in the worst case, it succeeds the Death Star as the expensive, long running, Star Wars OT play set.
8.) Red Five X-Wing - Released in May 2013, I expect R5 to retire this year but I'm not sure when exactly. It does look like it could be imminent though.
9) Death Star - Just kidding, not even gonna touch this one.