The July launching rumors of the Galaxy Tab S3 actually emanated from the fact that the first device in the lineup, the Galaxy Tab S, was launched in July of 2014. Its successor, the Galaxy Tab S2, did not come out one year later but it was announced by Samsung via a press release in July 2015.
It is likely therefore that Samsung is just waiting for the official release of the Android 7.0 Nougat before it rolls out the Galaxy Tab S3 to make it a really great tablet and allow it to stand toe-to-toe with the tough competition in the iPad Pro and the iPad Pro 9.7in.
Apple is expected to take the cue from the Galaxy Tab S3 in the development of the next iteration of either the iPad Pro or the iPad Pro 9.7in, although there are still reports saying that the American tech giant might still consider dropping the iPad Air 3.
Samsung has yet to make an announcement or statement or even a press release regarding the Galaxy Tab S3 so all reports, leaks, and rumors about its upcoming flagship tablet are mere speculations at this time.
It is also a possibility that the Galaxy Tab S3 might come out along with the Galaxy S7 Edge+, whose predecessor came out in August of last year.