Many good points raised.
For me, both the collecting scene and club attendance will continue but I'm convinced the nature of many nights will change in the UK toward the structure of nights that are dominant in Europe, which play an eclectic mix of tunes and attract both younger crowds and dj's.
From what Callum is saying, the night he promotes does tend to follow that approach. This, of course, does not exclude more mature attendees nor does it mean the end of oldies or rare soul venues that attract younger attendees.
From my experience, with my 20 year old, who is very much into the music we love, this more diverse playlist approach is more attractive.
Ultimately, it will be diversity and quality that will generate interest and ensure longevity (I Hope )