I, for one, like this idea, altho it needs tweaking.
First off allow all chars to transfer. even tho it would be designed for 50+ there is no reason to not let lowbies get wiped.
Secondly, I like the "no return" policy. This ensures those who have those "perfect built 50's" to stay and do whatever makes them happy and lets those who want to continue to upgrade their builds happy too.
Now to make it a separate game, no. an expansion yes. This allows new graphics and perhaps engine to be initiated without screwing up the original.
I like to see continuation and advancement, because if you're not moving forward you're stagnant. more content is nice but lets face it you played the game to get to level 50 in the first place, why not continue if at all possible?
and "IF" they did indeed actually raise the cap in this fashion where you could stay behind with your perfect 50, would you?