For the new *DBL gametype how about something that combines siege and warzone.  You have the 2 siege bases and a warzone in the middle.  The game is played like siege but you have to control the central zone before you can take the enemy base. 

The other catch is that both siege bases remain invisible on the command map.  When your team takes control of the central base, the opposing teams siege base becomes visible on the command map.

You can lose control of the warzone so you need to re-gain control in order to take the enemy base.