Come on people, this is all getting over-complicated. Now, for skywhales to have evolved naturally there would have to have been sky-beasties for millions of years, and most people seem to be saying that they have come about after the great war... So, I think it's far more likely that the Republic got bored someday and attached a balloon and engines to a whale for a laugh, it's easier than building a whole ship, plus in desperate times you have a reliable food source. (Plus who's going to shoot it? It's a freaking whale, everyone will be to busy gaping)