They were not really clear about this. It seems the way they said it you you just add to the server and you chose when you log in which map you want to play. She seems to confirm that later. Not sure.
I have my own server so I would like to know. There is no way I am changing the old map to the new one.
Until I am sure you can have both on same server I am not buying the new map. Not worth for me at all.
What make me think you can have both is I don’t see them spend more money for different servers with only the new map. If its not the case you can expect them to close servers. I hope they will make it more clear about this as even people who don’t have their own server would like to know what will happen to the official servers they are on right now.
Hopefully we get that answer before the release of early access on the 15th.