They stated that AV will become a 25-man, instead of a 40-man.
And that all BG's will be 10, 15 or 25 players.
And the largest group that can queue together will be a 5-man group.

I'd suspect if you want a rated battleground, you'll be forced to choose the random BG.
Which would make premades even harder to build.

Sure the opposing side can have a 5-man 'premade' group.
And they might even have multiple groups in a given BG.
But your side has the same likelihood of this.
And we are already a highly coordinated 5-man premade.
So the only thing certain in BG's is your side has a single premade.

I have a lot more fun in battlegrounds against random masses, then in arena against focused opposition.
Battlegrounds are chaotic, and aren't always 5 vs 5, you'll find 15 vs 2 or whatever.
Plus in BG's you can mix it up, recap bunkers/towers or rush the end base etc.. not always the same game every game.