There is no comparing this to BBM, WhatsApp, FBMessenger, or any others. If Apple brings this to Android, it WILL be the most popular messaging app on Android near instantaneously. It does not make sense, but it would make a lot of Android users happy. It doesn't make sense, however, because it is one of the few reasons I am still with iOS rather than Android...
No!! No!! No!! If iMessage will be in Android and if you download it, it is like you're showing that iMessage is better than the stock message app.
Multi platform iMessage is absolutely necessary for Apple, but it may come a little too late. Unless it has compelling new use case and functions; WhatsApp, WeChat, Snapchat and FBMessenger will be dominating the scene for a while.
As I have a number of friends and associates using Android, and frequently not being able to text me, this could be a solution to a long and aggravating problem. Fingers crossed!
It makes sense to push out to other platforms. Blackberry shot themselves in the foot, their roll out of BBM was about 5 years too late! in the current realm of media apps (line, wechat etc) they kind of have no choice but to open up that ecosystem to android. When Allo and Duo come out Android will no doubt push into apple territory.
Remember Blackberry (RIM) releasing BBM to other OSs?