I actually 100% agree with your for a new DBMS and share your frustration with vendor-specific features and lock-in. At that level, it's often actively counterproductive for insurgent DBs - ecosystem tooling needs more work to interface with your shiny new DB, etc - and that's why we always see anyone who starts with a non-standard SQL converge on offering ANSI SQL eventually.
I think an application that exposes a curated dataset through a SQL-like interface - so the dashboard/analytic query case described here - is where I think this approach has value. You actually don't want to expose raw tables, INFORMATION_SCHEMA, etc - you're offering a dedicated query language on top of a higher level data product offering, and you might as well take the best of SQL and leave the bits you don't need. (You're not offering a database as a service; you're offering data as a service).
