I just got to the section on destinations ("Stores"). Very cool. If you're planning to offer an Enterprise plan where you manage the infrastructure for your customers, we can deploy a dedicated white-labeled deployment of Splitgraph Cloud to any of the three major clouds. Perhaps you could find a use for that in your backend infrastructure.

ETA: Also, if you can write to Postgres, you can write to the Splitgraph DDN [0] with most DML and DDL statements, including INSERT, and CREATE TABLE. So even without any FDW, you might be able to add Splitgraph as a "destination" for your users (who would for the most part just need to provide an API keypair).

[0] https://www.splitgraph.com/docs/add-data/from-ddn