The old rating will stay active.
Next to that the new rating will run upon all the servers that are being tracked with this new method.

For the servers :
Our new tracker has the annoyance of always needing to connect.
Therefor we don't force it upon any server, if they like our new tracker they can always contact us and we will be more then happy to add them to the list.

So if your favorite server is not showing K/D's ask the server admins to contact us

Somewhere in the future there will be some more rules about adding new servers but that isn't decided yet.