Looks very cool. Can see a use-case for it at Sky Ledge (IoT/operational insights platform) [1]. To date, we've been building out data ingest from devices for our customers, and for that it's easy enough for us to spin up a service (for more complex use-cases) or a Lambda (for simpler use-cases) to perform the transformation.
However, we're at a stage where we're focusing on developer experience and allowing anybody to create their own "control rooms". Ingest is a particular pain point (we don't want users having to spin up their own servers/lambdas to handle ingest).
Something like DTL where users can define their own transformation schema would be ideal. The syntax might be a bit esoteric and we'd probably want to support both uploading the transformation schema and also composing it via UI for less technical users.