It all depends on what is released and where the technology is going. There are a few things that would have me jump the gun on an upgrade if they became available and useful:
1) Some way to have a video output from my phone so that I can do PPT presentations, screen sharing, or play videos from my phone to a TV. I don't particularly care if it is a physical connection, or WiDi, or some form of AirPlay, I will find a way to make it work for me. This would be hugely useful for work and would be the last feature needed in order to fully replace my laptop.
2) If a hardware upgrade is required in order to get Wallet to work for NFC payments from my bank acct then I will do it. This feature is so important to me that I will switch platforms if it is not in working order by the time my next upgrade comes around. My phone is much more secure than my cards or cash in my wallet that someone can just run off with and use simply because my phone has a password to use it, and another password to use the wallet functionality. I would be much more annoyed if my phone was stolen, but I am fairly sure that I could disable my phone faster than they could get into it and use it compared to cash and cards.
3) If some monster games come out that I get addicted to, but require better hardware than I have, then I would upgrade. However, it would seem that most games are not that graphically intensive, and the games that are graphically intense tend not to lend themselves to being fun to play on a touch format, so I am fairly sure that this will not be a problem over the next 2 years.
All that said, when the contract is up and it becomes available to have new phones, then I will ditch my L920 at the drop of a hat. I love it and all, but I am sure there are going to be much more impressive phones by the end of 2014, and the whole point to paying a contract is to get that cheaper up front cost on new phones, so I intend to use that liberally.