And where exactly is the rule that states that? No rule... no dice. I hate to pull the RAW (rules as written) card, but there it is.
The old model is of the same name and legitimately produced by the same company that created and maintains the rules of the game. It ticks all the boxes. It was fielded and perfectly valid before the new model was released, so unless there is a written rule that
explicitly forbids it, it is fair game.
Imagine spending good money on the old model, lovingly painting it up and building an army around it only to have some neckbeard tell you that you can't play it because the new model was released just a little while ago. I'd tell him to happily move along and find a new table to play at. Then again, as I said before, I wouldn't be playing AoS in the first place, so it's a moot point!