Ha, I had a bike shop employee (well, not really a bike shop, more of an 'outdoors store') try to convince me and my friend that 'disc brakes are the future, in two years ALL bikes will have disc brakes'. Thankfully it's not a bike shop I frequent very often.

I wouldn't worry too much about anything going obsolete on your bicycle. Drivetrains, brakes, shifters can all be replaced pretty easily. Out of style is another thing though...