Yes, your approach seems fairly viable . Here are some thoughts.

Step-by-Step Viability

User requests - Supported via Mosaic AI Agent Framework + ResponsesAgent interface
Metadata retrieval - Unity Catalog Functions can query INFORMATION_SCHEMA tables directly
Fetch SQL from repo - Databricks Repos API + Databricks SDK in Python UC Functions
Modify & test SQL - LLM-powered modification + SQL Statement Execution API for testing
Push to repo