Add the ability to create data sources for the Connect ening using some JSON based protocol. Not to query arbitary JSON files or services that return JSON data, but a standardised protocol to query datasources using JSON elements, and returning JSON elements.
This would open up MariaDB to a much wider pool of datasources by enabling data source developement in any language, not just natively in C++. Along with the M-SELECT feature request (MDEV-22308) would make MariaDB a key component in connection a much wider range of data sources efficiently.
It would also enable more souce specific optimisations to be done as more knowledge about the end user's actual needs would be passed down to the source, instead of doing multiple interrelated queries.