There aren't any plans for Spring Cloud Deployer SPI implementation for ECS. Likewise, there aren't anything officially scheduled for SCDF implementation either.
The SPI abstraction is setup for easier extension and we encourage users to implement for different runtime platforms where they see fit. For example, please check out the community implementations of SCDF for Nomad and Openshift platforms.
Does it make sense to consider using ECS as a runtime platform for Spring Cloud Data Flow?
From the surface, it looks like the primitives to orchestrate Docker containers is in ECS. We distribute Docker variant of stream and task app-starters, too. Apart from this, routing, LB, logging, security, HA, and resilient orchestration of apps (embedded in SCDF streams/tasks) matter for production deployments. You may have to dig into these specifics for decision.