Impossible because Eevee would have been able to evolve with it in the earliest games then
GF won't contradict themselves that much
Piloswine has been able to learn AncientPower since both Pokemon and move were introduced. Lickitung has been able to learn Rollout since Generation II. And not until Generation IV has leveling them up with those moves actually done something. That right there proves that GameFreak doesn't give a Raticate's rear end about continuity with evolution methods.
Then how would we evolve Eevee into Glaceon.
New generation, new items. Like it's really beyond GameFreak's means to invent a new ice-themed evolution stone.
Come to think of it, Sun and Moon stones for Espeon and Umbreon are also starting to sound feasible, but in those cases, I'm a little skeptical somehow.
Let me introduce you to my level 100 shiny Magneton. Magneton reached level 100 way before Magnezone was ever thought of, and thus could not be evolved.
Say you have a level 100 Pokemon with great IVs, but you screwed up its EVs. And since it's level 100, EV training is out of the question. OR, say you have an unevolved Pokemon at level 100, and now you're changing your mind about keeping it unevolved, but it needs to level up to evolve.
No one trades entire boxes in one sitting. I've never traded more than 10 at once.
I have 14 boxes of level 100 EV trained Pokemon, and a box and a half of legendaries, which I've traded from Pearl to Platinum, and from Platinum to HeartGold. Plus a box of reserves I use for in-game purposes. It took me WEEKS to make the full transition from Platinum to HeartGold. Faster trading/ability to trade entire boxes at a time would be an Arceussend for me when it comes time to trade them from Black version to the inevitable R/S remakes.
@Snowyarticuno: Yes, that's all very well, but not everybody does that. Suppose the Pokemon in question you got in a trade from someone who doesn't know diddly about competitive battling. Or if you yourself raised it before you knew about EVs or IVs. Or knew about an evolution that requires leveling up. Or realized you wanted it to evolve after all. I've wanted an item like this ever since I realized evolving Magneton required leveling it up.