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.
subgridto level 2 of Grid would create accessibility issues that would be hard to rectify even after level 2 is released. TabAtkins stated that he still believes that the inclusion of
subgridin level 1 will cause too much of a delay to implement before shipping. The discussion will continue on the mailing list with sylvaing recommending a focus on use-cases instead of general speculation on what adopters may or may not do.
keyframesall revolved around reaching consensus on how browsers implement the spec. Sylvaing will solicit feedback from the browsers to ascertain the best path to compatibility and then move to solve the other issues.
custom-identvalues, but there still isn’t a clear path on how to decide what other keywords should be excluded. Discussion will continue on the mailing list.