Paste (super+v) should duplicate text if selection = pasted text

Why not just hit paste twice? Or use the duplicate command if that's what you want. Doesn't seem logical to build in special cases to the paste command that change its behavior when it's more valuable to behave consistently with other apps, imo.

"Why not just hit paste twice?" 

Didn't understand what you would achieve with this..

Anyway, there is no utility on pasting something on top of the same thing, so of course no one does it. Therefore, no consistency would be broken, but functionality would be added.

The best interfaces are the ones which add functionality in a subliminal way, not necessarily in a explicit form. Why memorize an extra shortcut, or take extra space on the keyboard, when it could be achieved with the combination of 2 familiar ones?

If you prefer the duplicate command, you can keep using it :)

Very much disagree with "no utility on pasting something on top of the same thing". I will often copy and paste an identifier on top of other copies of it just to make sure I haven't made a typo in my code. I very much expect it to do nothing if they match because that's exactly what I want.

then I stand corrected :)