The next thought in my addled brain is that since we only really use the egress side of it, perhaps some of our neighbors would enjoy affordable 10G internet access…
The reverse here is maybe interesting too - a lot of WISPs have a bunch of spare 'upload' (from their perspective) bandwidth available, and by definition it's very geographically distributed, maybe that would be of use to CDNs?
I'd love to chat more about this if you're interested. Email in my profile.
It might be different if the WISP has connections to local residential ISPs that aren't well connected to local internet exchanges (or there nearest internet exchange isn't very near) so the WISP facility offers a way to get (network) closer to more users.
I could also see some potential for mixing traffic streams between a WISP (or several) and a CDN to try to balance traffic flows enough to qualify for peering with networks with restrictive peering policies; however, they also often have geographic requirements that might be harder to meet.