Preview at WWDC likely in June, followed by September launch.
Apple Seeds Third Beta of iOS 9.3.2 to Public Beta Testers
Beta testers who are taking part in Apple's best testing program will receive the iOS 9.3.2 update over-the-air after installing the proper certificate on their iOS device.
Those who would like to participate in Apple's beta testing program can sign up through the beta testing website, which gives users access to both iOS and OS X betas.
As a minor 9.x.x update, iOS 9.3.2 appears to focus on performance improvements and under-the-hood bug fixes to address issues discovered following the release of iOS 9.3. We don't know all of the fixes that will be included in the update, but a significant Game Center bug appears to have been fixed.
iOS 9.3.2 beta 2 also re-introduced a much desired feature -- the ability to use Low Power Mode and Night Shift simultaneously for power saving features combined with blue light reduction.
No other outward-facing changes or immediately apparent bug fixes have been discovered in the first three developer betas.