When viewing changeset history I tend to think about changesets in terms like "that is the checkin where I merged/rebased from /other_branch". That kind of context is sometimes lost in the Plastic views:

• In 2D History if a merge is unrelated to the selected item then the merge arrow is not displayed.

• In Branch Explorer if the /other_branch is hidden by filter, the merge arrow is not displayed.

Not displaying the merge arrow in these cases is logical since the /other_branch is unrelated or hidden. However, I'd find it helpful to have some kind of (optional) visual indicator that an incoming merge is part of a changeset that is already displayed. (This should not affect the "Display only relevant changesets" option.)

Perhaps you could render the incoming end of a merge-arrow and make it "fade away" or become "dotted" further away. Or display a special arrow icon to indicate the non-displayed merge. It would help bring the displayed changesets into context.

Also, the "View history" and Changesets views could benefit as well from having different icons for each changeset line depending on whether there's an incoming (or outgoing?) merge etc. As it is, the icons in these list views are not really used to their full potential since they are all the same...