Will release on the day of OS X Mavericks release
I think it'll be released in September/October because the leaked benchmarks of the upcoming rMBP (https://www.macrumors.com/2013/06/2...ro-benchmarked-with-modest-performance-gains/) show that the pre-release model is running OS X Mavericks. Apple would only test the version of OS X that they're going to ship with the Macbook Pro. So, it's very likely that these Macbook Pros will be released on the day OS X Mavericks is released and will be initially running OS X 10.9.
I think it'll be released in September/October because the leaked benchmarks of the upcoming rMBP (https://www.macrumors.com/2013/06/2...ro-benchmarked-with-modest-performance-gains/) show that the pre-release model is running OS X Mavericks. Apple would only test the version of OS X that they're going to ship with the Macbook Pro. So, it's very likely that these Macbook Pros will be released on the day OS X Mavericks is released and will be initially running OS X 10.9.