I don't think "source available" is really that viable of a model. MS tried that with a lot of their developer offerings before more became truly FLOSS, specifically in the .Net space.

In the end, I'm less likely to trust/use ANY non-floss software/services that doesn't have a clear and clean exit path. I can use CockroachLabs (CockroachDB cloud) as I can exit pretty cleanly to self-hosted PostgreSQL with other models. I can abstract the usage of say DynamoDB to target other options relatively easily as well.

That said, tethering deeply into rented services, or commercial+floss providers can only hook you in the end if things get too dicey. And you only need to look at Oracle and IBM/RedHat as examples of the hook you and reel you in approach. A lot of businesses are also pretty deeply tied into a given cloud platform. They all have nice to have, relatively easy to use features/services. If you don't have an exit strategy, you better have a fat wallet. It's not that it won't still be painful to exit, but without at least a strategy, you're trapped.