Interesting post Oolak.
This site and the the threads on MTBR are the sole reason I built mine up. Other people are doing it so why can't I ? In reply to your last question, I completely agree that DIY is only going to get more popular the more positive experiences are shared.
Spare/replacement/ugrade parts have always been available. Now we can add cheap Carbon frames and parts to the mix ! With this and the sheer amount of internet knowledge via forums/youtube etc it is making people more aware that self builds are achievable.
However I don't think its going to be a massive disruption, just a slight shift of needs.
Maybe less complete bikes will be sold but the LBS will still be relevant. I think I would've spent less time and money in my LBS if I had've bought a whole bike.
As I wanted a top end spec FS I would have had to shop around to find the best price, this would have meant buying online to save money. When you're spending a few £K a few hundred pounds discount is massive. In theory I would've bought a bike ready to ride and had little need to walk through the doors of my LBS, obviously this does not help my LBS but thats the reality.
Now I have built my own, most parts came via the internet and post due to me being abroad and I had the time to browse and purchase at a reasonable price, then it was time to assemble the bike and thats where the LBS came in. BB and cassette needed fitting, then a wheel build with a new hub. This led to skewers, seat post clamp, stem, lights, clothing, fluids, tools etc and most importantly advice coming from the guys working in the shop ! I now have a relationship with my LBS that I don't think I would ever of had buying a whole bike. (I doubt I would have the same relationship even if I had bought a bike through them !)