Rust, Go, Python, and C++ Iceberg implementations change who can write the format. Why multi-language clients matter more than another JVM engine.
Iceberg v4 is really about making the cost of a change proportional to the change. The principle, the current tax, and what the redesign pays down.
Can seven Iceberg REST catalogs run the same DuckDB script? What the protocol makes portable, what still differs, and a test matrix you can rerun.
Remote scan planning moves Iceberg file selection into the catalog. What that changes for engines, governance, and operational cost beyond query speed.
