I believe Apple needs to build iMessage for Android. They have lots of reasons not to build it but I believe that have at least one really good reason to do it.
Apple has already acknowledged Android’s importance by building Apple Music for Android (I won’t count the Android to iPhone migration app). This was a sound business decision, the same was building iTunes for Windows was a necessary move. The sheer number of Android users will bring about more revenues and will help prevent services like Spotify from generating a lock-in effect for the hoards of people moving from Android to iOS.
iMessage is different, though. iMessage does not generate any profits (yet), and has simply been a value-ad for the iOS (and Mac) customers. They could have continued down this path, but something changed recently: Apple has doubled down on their fight for privacy. Tim Cook’s resolve and public appearances arguing against FBI’s request to build a backdoor in iOS is unprecedented. He even gave the first ever interview from his office on 1 Infinite Loop.
No other player in the space advertises privacy as a core product “feature”. Apple needs it not just because it is a differentiating factor, but because they truly believe this is the right thing to do for their customers.
The fact of the matter is that Apple’s customers interact with people on other platforms all the time, and not all the apps they use to communicate with their friends on non-Apple platforms are secure. Sure, WhatsApp provides end-to-end encryption, Telegram does too, and so do many other apps. But none of these apps are controlled by Apple.
Building iMessage for Android will give Apple the ability to tell its iPhone customers that all their communication with their family and friends can be secure.
There’s an argument to be made, that for this to be completely accurate, Apple would also need to build iMessage for the web.
A bonus reason (speculation), is that iMessage is one step away from becoming a transaction platform (much like WeChat). Person-to-person payments could be one such type of transaction. In order to be successful, such a product needs to be available on as many devices as possible, thus making Android impossible to ignore.
p.s. If iMessage is to be added to Android, then FaceTime will most likely be added, too.