I believe the success of NXT Takeover: Brooklyn last year configures into how Summerslam is being promoted this year.
Brooklyn was rated, by NXT, as the best show of 2015. What better way to kick off this new era than to feature four of NXT's most successful products in the brand new Universal and Women's championship matches, respectively?
The Brooklyn crowd will go apesh*t because they love Bálor. They did last year and they will this year. WWE has a Summerslam deal with the Barclay's Center running through 2017. They ought to feed that beast while its hot. With Reigns' failed drug test to boot, the stars sort of alligned for Bálor.
Rollins will make Bálor look great then go onto hold the Universal title for a ridiculous amount of time. Rollins, NXT's crown jewel, will have the task of establishing this championship as significant.
Edit: I realize the Woman's Championship isn't that new but given that it has it's own distinct lineage makes it very fresh.