Daniel Friesen let us know:

For reference this is the RFC that was discussed in my thread on the subject.

https://www.mediawiki.org/wiki/Requests_for_comment/Abstract_table_definitio...

Should probably dig up some gmane/archive links for both this and that discussion and add them to the RFC page.

Excellent, thank you for that link. That mirrors a lot of my thinking. I'm going to take a fresh look at my data type issues with that page as a guideline.