That would mean that they need to maintain 2 different systems and make new servers. Which will need quite a heavy investment and more work from the staff team.
Keep in mind that adding new lvl cap, activating higher lvl quests and making sure bugs do not happen on 2 different systems just is to much to ask for.
I was thinking more that the old server would just not get any more updates. That this is it (like with old software with an end of life).