Ive been playing wow on and off for a few years and have noticed that bgs (and now wintergrasp aswell) is never a balanced affair.
Im still getting games that start 15vs8 , some factions get stuck with 10-15 min ques and wintergrasp can be a 5 vs 100 battle. The solution? throw all que'd players into a random draw and split teams evenly. Srsly wow can pretend there is some big open war between the alliance and horde but everything in-game contradicts that anyway. In most pve events alliance and horde work together , on most pve servers alliance and horde help each other at times. Even on pvp servers i see it happen frequently. Seriously i hate some races of my own faction more than some of the enemy factions races !!! , this in itself is reason enough.
Basically doing this would eliminate the "omg horde always win av" and "My server never wins winter-grasp QQ". I admit with regards to winter-grasp some fiddling would be required to keep the buff for winning applied fairly. But bgs would be an easy thing to fix with this.
My final point? well ive seen a crap ton of people xfer to the other faction since the option became available. Many suggest its because on their battlegroup , their faction never wins bgs and the whole experience is maddening. I am privy to be in a situation where i have both alliance and horde chars on such a server and one side has massive ques while the other never wins =/.