Hard to call it a successor of SMS when have the world uses iOS which does not and currently has no plans to support it. So more just another service rather than a replacement for SMS which is a way for all phones to communicate with each other.
(aside: is there a name for the extension of Hanlon's razor where one shouldn't attribute to stupidity a simple miscommunication?)
[0] https://www.statista.com/statistics/755625/iphones-in-use-in...