A 780 will definitely be out dated in 4 years, with the rise of high resolutions on monitors being the norm , even 1080 resolution in 4 years time is going to become retro, with 1440 becoming very popular for monitors today and 4K starting to roll out , you need a a couple of 780's or titans for the latter to run these optimally to get high frame rates.
In 4 years time a 780 will become mid end, look at the advances already with AMD's 290X and just wait and see what Nvidia is going to do with their 800 series.
The performance crown gpu will always get thrown off its top rank , there's always a newer card and refresh around the corner to beat them , as you can see already Nvidia are topping their 780 with a 780ti and the newer series from both companies are being released sooner than they used to.