This would be a monumental move for Apple. Really, even the most diehard Android fanboy excited by this news doesn't understand how big it would be (for Apple).
Since it was founded, Apple has been a devices company. They made great software and various services (with varying degrees of success), but it was all to support those devices.
They did actually have one world-beating service: iTunes. In fact, many people credit the ITMS with most of the iPod's success - it was an excellent, competitive service and was integrated well. But Apple always looked at this from the device perspective: iTunes was there to sell iPods. They didn't really nurture it as the excellent service that it was, and they're having to play catchup as they realise that it's okay to also be a services company.
With iMessage, they did a similar thing. They kept it closed and relatively restricted as an iOS selling point, but instant, asynchronous communication is a valuable service in its own right. There is lots of talk about bots and integrations with 3rd-parties. That's shareholder (and user) value that Apple is leaving untapped. If they do that for long enough, iMessage will become irrelevant, too.
This is Apple's business strategy waking up and getting with the 21st century.