That's not entirely true (your first point). Both my wife & I have met all sorts of acquaintances and what became good friends through interests that started with coincident physical locality: gyms, clubs, church, children's sports & school, etc. I don't think the problem exists completely in the way you seem to think. One potential mental block could be that spontaneity is a key piece of the equation. I argue that the vast majority of humans are not spontaneous and that's a hugely overrated attribute, if so.

I 100% agree with your second statement, though, that the future of social networks will focus more on the social and less on the spam & social signaling.

I'm not sure how you can say this when Meetup has been around for years. It does exactly what you describe.

By the same token, what does Facebook do that MySpace didn't?

My comment was in response to:

"the problem of putting together complete strangers with shared interests and coincident physical locality really hasn't even been attacked except in very constrained use cases (i.e., dating services)."

When clearly Meetup have both attacked and been very successful in "putting together complete strangers with shared interests and coincident physical locality". That's exactly what they do, would you not agree?

I'm honestly not that familiar with Meetup. I thought it was basically just a calendar for keeping track of local events. Do people maintain profiles or personal pages on it?

The problem of putting together complete strangers with shared interests is solved by Reddit.

No more so than it was solved by Usenet, though, or by BBSes before that.