From the MacDailyNews report:
Apple will announce that iMessage encrypted text messaging is coming to Android users at WWDC next Monday at WWDC 2016, according to a source familiar with the company's thinking.
This will make it possible for Android and iOS users to communicate securely as iMessage features end-to-end encryption – even Apple cannot access users' messages. Currently, iMessage is accessible through the Messages app on an iPhone, iPad or iPod touch running iOS 5 or later or on a Mac running OS X Mountain Lion or later. In February, Eddie Cue announced that the number of iMessages sent surpassed 200,000 per second.
This year's reports on WWDC software surprises has been tamer than most, but there's always a chance we'll see more over the next couple of days leading up to the keynote on the 13th. Although some people have hoped for iMessage on Android for a long time, Apple has never been big on cross-platform support.
Apple Music shipping on Android, though, shows that services might become the exception. So, never say never, but also believe it when you see it on stage.