SG True Queen Jezilina
I have to agree with him. As cute as it sounds, the storyline would be a bit boring. Plus we must consider Usagi. How would she feel? She already got on Rei when she was flirting with Mamoru. And plus Mamoru is in love with Usagi already. The lovestruck moon princess and the earth prince already have a history. And what about poor Zoisite. The general who was in love with the Mercury Princess? What happens to him? These questions demand to be answered.
Well even if Mamoru and Ami were a couple, it's not like this would exclude all other characters in the series. They would still be fighting evil things and etc. Besides, they would have th drama of still having to separate across countries, and also their friends and such.
Usagi would probably be depressed about it, but I'm only going on concept here. I guess in my head it would go like, from the beginning as Usagi having Ami's personality/name and basically switching the characters. That idea isn't that far fetched, since Ami is Japan's favorite Senshi.
The Zoisite thing, well, depends on what side of canon you are. TECHNICALLY it's a fanon couple. Then again, if you're like me, it's in the manga so it counts. Of course in my head I'd imagine the characters being switched, so Usagi would get him. Which actually makes more sense, since they're both flamboyant and fashion driven and etc. Oh Jeez that is weird XD!