Microsoft's upcoming arcade environment, Game Room, faced a huge potential downfall in the way that every game that was due to be released through Game Ro would need to be classified by the ESRB. Something which would have delayed games quite a lot.
However Microsoft have swiftly solved this by having Game Room as a whole rated, the virtual arcade will b given a E10+ rating. This means that every game released onto Game Room will be of a rating no higher than that thus reducing the need for them to be individually rated and speeding up release times.
Just don't expect to see such titles as Mortal Kombat or Metal Slug in there anytime soon. But you already have the option to get them on Xbox Live Arcade anyway should you wish to buy them.