By the way, do you think I can make the same request for MC 16 ?
You just did. But it didn't go anywhere last time, so we would need to get a discussion going and hope others show an interest.
I think it's safe to say it's not the sort of thing that's likely to be implemented if it requires some significant change to how everything works. It would be nice if the developers could give some hint as to whether something like this might be feasible or is just wishful thinking. Based on Jim's recent explanation of how they consider these things, I can offer a suggestion: If they think the idea sucks but don't want to tell us, they could just tell us it's not feasible for proprietary technical reasons.
From a usability point-of-view, I can see it being implemented in such a way it wouldn't adversely affect anyone not interested in using it or who might be confused by its existence. If it applied only to list field panes, items were selected for exclusion (and de-selected) with a Alt-Click and their selection indicated by strike- or grey-out, it wouldn't get in the way of "normal" use of the panes.
There is something else which may be both a usability and technical issue. Panes do not work in isolation. Generally, when a selection is made in one pane, the others are updated to show only the values present in the current selection. A user's expectation would be same if this were being used. That seems simple enough, but we don't know how things work under the hood—so who knows?