Vintage music scenes are inextricably linked to record collecting though, and for good reason.
I dont think so many people would be attracted to the culture of DJing if it really was reduced to downloading mp3s of known music and 'putting them together in an order that works!' - there is some skill to that part of DJing, but not much, and it's a skill that is a lot more easily acquired than an interesting record collection is.
The thing about collecting as a component of DJing is that it is the creative aspect - the bit where you can genuinely do something no one else has, the bit where genuine cultural influence can be in the hands of a normal person. That is - finding unknown or barely known music and presenting it to the world.
That and that alone is the real pay-off for djs, filling dancefloors is great, but without the process of bringing new tunes through, is creatively vacuous, and makes you little more than a hipper wedding DJ.
Considering that, it stands to reason that when there is the sense that there is nothing realisticly left to find, for the average collector / dj, that is fresh to their audience's ears, the thing will gradually fizzle out. At that point, record collecting will be reduced to an individual enterprise, based on individual collecting goals, will lose any relationship to social culture and will fizzle out too.
Thats the reason tbat the creative end of the soul scene has explored new genres and styles, and is why the mod and r&b scenes are still relatively creative - they're a generation or two behind northern soul and have a wider musical scope, so, whether 20 or 70, theres still things to find for the DJ that will let them do something individual and creative.
Listening through tunes on youtube or downloads lists, and chosing the ones you like isnt only tbe preserve of young people anyway - why would that be more popular with a 20 year old than a 40 year old?? - but in any case I can never see it giving people the sense of expression and adventure that djing via record collecting does.
When every decent tune is either pressed or digitalised then djing as we know it, and the culture that goes with it, is over; it might well be the case, as you suggest, that a new culture of selecting tunes from a list and putting them together well develops, where I suppose effort and knowledge would come through in its own way, but it wouldnt be the competitive, creative and varied adventure that this, in all its variations, has been.