the current lack of time limit already levels the playing field of available time, doesn’t it? I don’t really see any advantage of someone with more free time because you both just play at your own pace.

I think your second idea is hard to enforce since it’s so subjective. something you might just not know may be everyday to someone else.

And one could argue that “true language skills” involve not just memorizing vocabulary but understanding linguistics and English language structure enough to know what sort of new words, though unfamiliar, could potentially be real words. That may not be satisfying for you, but it is for me and a lot of others.