> What I want is, for example, to press 'Transfer all pictures/music/whatever to Time Capsule' and just wait until it is done (via WiFi).

It's not an Apple product, but "Plex" can transfer your photos to your own harddrive/library if you buy the pro version. You can for example run the Plex server on your Mac or on a Raspberry Pie, and then let Plex synchronize your photos to your Capsule over wifi or 3G.