This is a page from the Cascading Style Sheets Working Group Blog. Some other places to find information are the “current work” page, the www-style mailing list, the Future of CSS syndicator, and the issue list on Github.
Do you want to know how the CSS WG works? Fantasai has written about:csswg, An Inside View of the CSS Working Group at W3C.
column-span
apply only to direct children of the multicol element however there was also concern about headings nested in sections and similar use cases. There was a desire to find out what browsers do to see if there’s already compatibility which would also lead to adding some test cases to the test suite.