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.
sup
and sub
has a very high likelihood of causing breakage. This should instead be filed as a bug against Fonts 4 or 5 as a proposal to change CSS. Any request should also have test cases to demonstrate what would be different between the current and proposed approach.