You select the public cloud vendor you want your machine spun up on. So no, if AWS has a full outage, it won't fall back to a different cloud. Failover is done at an availability zone level.

Since TimescaleDB is also open-source, if you want that kind of replication scheme, you can always install on VMs across clouds. However, as you rightly pointed out, network latency is a definite concern and impacts the feasibility of RPO and RTO.

One thing to add:

The Timescale Cloud does allow you to do is create asynchronous read replicas across different clouds and regions (with a couple clicks).

You can then "fork" a read replica (at any point in time) and make it a primary to start serving out of that cloud (again, with just a couple clicks).

That's not quite the same as auto-replication/failover between clouds, but getting pretty far there.

Can be done with an async-replication db like ScyllaDB. Or even CP db (just harder/slower).

Yeah! CockroachDB is also a really cool multi-cloud DB. That being said, they are really more for transactional workloads, and less purpose built for time-series.

I guess there are always trade-offs in the software world.