Personally, I'd like to have something like this:
A program in the PC that detects when the Nexus 5 is plugged in via USB that triggers an automatic backup/sync (copy + paste) of all/selected files/folders to the PC/Nexus 5/vice-versa. Or, similarly, an program on the PC (that could be partnered by an app in the Nexus 5) that detects when the Nexus 5 connects to the same wifi network where the PC is connected and triggers an automatic backup/sync (copy+paste) of all/selected files/folders to the PC/Nexus 5/vice-versa.
Anyone? I hate MTP by the way. It just doesn't work well for me. It freezes up my Nexus 5 or PC and just takes a long time to copy files. I hate the fact that USB Mass Storage isn't working on the Nexus 5.