IMHO gebruchts are a very different din than regular dinim of kashrut of basar and chalav for example… as in we don’t just keep those dinim every day of the week except Tuesday. However, many if not all of those who do not eat gebruchts DO eat gebruchts on the eighth day of pesach.
It is, no pun intended, a minhag chasidus, as far as I am aware. Someone who eats gebruchts is not (or shohuld not be) looked at as someone who has a disregard for halacha, or even someone who is being meikil. It is just a minhag, and therefore, considering how removed the sharing of keilim would be from the actual moment of “chashash” (and it’s in quotes for a reason) I never thought/ knew there was halachik basis for being makpid on such a thing.
I for one have heard in my shul that sharing keilim from kitniyot to non- kitniyot observers was not even an issue.