I wonder what the increase in tourism and population is going to look like

Yes, dm-cache is not new, but it just had a major new release. It now has a feature to allow many vms to share one cache.

I can't speak for the flashcache team, but I do know that one goal of the dm-cache team is to get it into the upstream for the linux kernel(I know this b/c I worked with dm-cache team last year).

That's great to know! Hopefully one of these projects will make it into the kernel soon, since this is obviously a very useful feature.