I play on 1440p just fine on all the games that I own. Even some older games I play that I didn't expect to support it already had it built in. As far as modding games to support different resolutions, I think that would be impossible. No game is the same as another and if it wasn't designed to run a specific resolution then it just wont run that resolution.
As far as down scaling goes, I dont see any reason why a game running at 1080p on a 4k monitor would look any different than on a 2k monitor. If anything it would look worse since you are stretching a smaller image over a larger resolution space. Another user talked about this same problem here: http://www.tomshardware.com/forum/id-2232285/downscaling-native-1440p-gaming.html...