Mesh networks don't really scale to continent size and there really isn't a lot of free/unlicensed spectrum to work with, it's already really crowded. WISPs do a lot with what they have to work with but it's still not going to supplant the internet without some major technical breakthroughs.

I do not think this is about replacing the current Internet and watching Youtube or Netflix using a mesh network.

It would be more about having a slow, free and backup internet available. Nowadays, we talk a lot of cyber attacks and WW3. I am pretty sure the Internet would be the first thing to go out if things would escalate (at least at the same time as the grid).

I am not sure how long a "modern" society can operate without connectivity. The idea of a mesh network is also very cool.