Uh... no. They wouldn't need to mirror everything this time. They would just need left-version animations for Link.
In response to this, I've merged these two threads. Aonuma's quote is in the OP. I do agree somewhat with your last statement, but from what Aonuma says, a lefty mode would mean either two games or less actual content on one disc to make room for the extra models.Where has it been stated that there won't be a Lefty mode? Like various others have mentioned, all you'd have to do is flip the display. Which is very easy to program and doesn't take that much space.
SWS still doesn't even have a release date, so it's far from impossible that they'll include such a Lefty Mode.