My view/hope is that at least for basic application level services, that the abstraction is going to be provided by containers and their orchestration platforms (e.g. Docker/Kube). It can credibly give you scaling, data persistence, network isolation, service discovery, load balancing, and with some work, a database (when packaged in a container with a persistent volume). An app using only these basic services basically has zero cloud lock-in.

On top of this there are many additional useful services that AWS, GCP and Azure provide. Using those does indeed give you some level of lock in, but only when these services are not available as a generic TCP/IP services (or not performant when accessed from a different cloud). This is where application designers need to make a trade off.