Sorry for seeming silly, but what are the two options?
When there is a rectangular selection and a single item on the clipboard the choice is to paste the single item into the first row of the selection or to repeat the single item in every row of the selection.
Although from #2317 comes the suggestion that if the clipboard is multi-line that successive lines get pasted into successive rows of the selection, so now there are three options grin
I might be too closed minded here, but I sincerely don't see the user case for the first one. And when I say user case I mean actual user base demanding this one and complaining about having the second one.