Thanks for starting the discussion.
First, when you said "locked", we need to clarify a few things:
- The parquet format is open, as the delta format is open too Home | Delta Lake
- You can read and write other type of file formats within Fabric. But yes, all the storage for Fabric engines is written in the delta/parquet format
- You can integrate S3 buckets and soon Google Cloud Storage into OneLake (Fabric Storage) through shortcuts.
- You can implement a data mesh architecture with Fabric, based on an open lake (accessible APIs and open file format).
- From what I understand from Iceberg
That being said, I woud like to understand more of your interest on the Iceberg format, and why choosing it over the parquet format (which are both open formats from Apache, and are note tailored for the same usage). Also, You can submit that ask to the Fabric Ideas section of this site, and get people to vote on your idea :).