For Ladybird - Andreas Kling called out that the vast majority of "easy tests" are passing and each additional test is going to be more difficult to come by going forward.

https://www.youtube.com/watch?v=-l8epGysffQ (1 minute - 4 minute)

As another comment pointed out, some of them will never be implemented on purpose. These tests aren't all backed by web standards. E.g. one test suite is for compatibility with non-standard Blink APIs

Also there are new tests being added all the time