It doesn't have to replace the current servers, it can be EU10 and NA10 or whatever is the number. Should be easy to do, you just make a server with both battle and siege maps in rotation, right?
Advantages:
- Community doesn't split up when some want to play battle and others want to play siege
- More variety in gameplay, you don't end up playing the mode you don't like because no one is playing on the other server
Disadvantages:
- Players might leave when the server switches to the mode they don't like
- Ratio of battle and siege maps will have to be constantly adjusted through trial and error