Well the ideas here are more about problems than about solutions. The problem  is basically the same: "There's currently no way to see only tags related to current selection, and only them", so hopefully you can see the reason for merge. Merged, these two ideas will get more votes than being separate.

Ctrl- and Shift- clicks will work the same way. Doubleclicking will just hide/unhide unrelated tags.

I just used the duplicate mechanism which is built-in in UserEcho. Mohanarun's request is there in the original form under "duplicates".

How about this suggestion as a (partial, but nonetheless) solution to the problem you describe?
http://roadmap.cintanotes.com/topic/23145-forwardbackward-navigation-filter-history/