Prediction: 6v6 will be the classic format, while Blizzard will further experiment with 5v5 as nu-Overwatch
Just a bit of a shower thought I had. It makes functionally no sense to run 6v6 and 5v5 simultaneously as seperate formats as the difference between the two are not nearly as substantial as their detractors would say.
So why run both? Because now Blizzard can offer a more traditional Overwatch format that appeals to the old heads while also having 5v5 as their staging ground to make substantial and bold changes to the core gameplay while still offering the original flavor for people who don't want to see such changes.
I personally feel like this is the best way forward if 5v5 and 6v6 are to co-exist.