From what i've seen and read, Blizzard are alternating days for more people to participate in arena and RBGS, so there will be more ques for both during them days, when it is not arena day, there will be skirmishes which i believe the community has been asking for, for a while now.
I personally like this idea, as it means i can level up alts for pvp and just leave them in their competitive pvp gear whilst i get the chance to Gear my main. Personally i found it boring and tedious gearing up 3-8 alts and this change means i can be competitive on all of them.
I see this change working positivity as it will stop win trading and make pvp competitive and fun once again.
From what we know right now I believe alternate days is indeed the current plan.
Everyone, please continue giving your thoughts on this feature but remember that the system is still in the works as we take on board your feedback, so try to keep it constructive :)