The 5x5 bag thing isn't exactly a new development. We've seen it since the first 2.0 concept screenshot:


The bottom right shows 7 5x5 bags. They've talked about how the different colored dots represent different types of items. Seven 5x5 bags along with mannequins seems like it'd be more than enough. Obviously that stuff is subject to change but for the people who think we'll just have one 5x5 bag, I think you can assume we'll have a few more than that.