In terms of the theory covered here it doesn’t really matter whether the edge is a cloud region, CDN, server in your building, or personal device. I don’t think any of these havent been tried as nodes in a distributed transactional database. It’s kind of just a semantic argument - the network failure rate, availability, and capacity to scale horizontally within your “edge” node are just parameters.

Imagine this: within a CDN’s compute you try to serve distributed db transactions optimistically then fall back to your big cloud region when it fails. The CDN is kind of a write-through cache. You still have to address the CAP theorem distributed state challenges of synchronizing state and making a consistency/availability/partition tolerance tradeoff, and it seems like a reasonable use of a CDN.