I have! However, (correct me if I'm wrong) they don't solve the database issue. You still have a single region with a "leader", and other regions just have read-replicas.
Shopify uses exactly the same model we (Fly.io) do, it's a slightly more evolved version of what you're doing. They run leaders in multiple regions with read replicas scattered around, and then assign the most appropriate leader region to a store.
CockroachDB and Spanner let you move ranges of data to different "leaders" within the cluster. If you model your schema well, they work great. But you do have to worry that queries aren't spanning regions or you end up making everything slow.
The Fly.io magic is the proxy layer that replays entire HTTP requests to the leader region. It works surprisingly well. If your databases is even close to half reads and half writes, something similar may work nicely.