This one pretty much made me lolz to the max, and makes terrific sense why more evos is a generally bad idea. I'd definitely start getting concerned if Game Freak tacked an extra evolution on Charizard, that's for sure.
The power creep extra evos would usher in would throw the metagame out of whack, and pretty much gift everyday pokemon with BSTs on par with non-mascot legendarys, or something...not a pretty sight.
It'd only work if the series decided to give itself a true RPG overhaul, and make legendarys with 1000+ HP, multiple hold items like PokeArmor or the like, and increase the overall BST of all pokemon across the board...but let's face it--this is Pokemon we're talking about, and they rarely switch things up so radically.
Legendary Evolution, though, sounds like new and definitely interesting territory. Gen 6 seems to be playing with themes focused on DNA, and Eevee is getting an unusual amount of attention ingame and on the official site (days after the reveal of X and Y, Pokemon tweets ''Quiz time! How many possible Eeveelutions are there?'')
Not saying we'll get evolved legends at all, Especially since it'd put pokemon over Arceus' strength, but... we're highly likely to at least get a new Eeveelution. That cutesy fox should be as far as multi-evos ever go, for the franchise's sake.
...A wise one once told me love was like a pokemon battle. You can fight it, you can run away from it; or you can end up without any balls when the opportunity arises.