Apple is not changing anything about how iMessage works, it's clear in their statement in the article you linked: > We believe RCS Universal Profile will offer

Apple is not changing anything about how iMessage works, it's clear in their statement in the article you linked: > We believe RCS Universal Profile will offer a better interoperability experience when compared to SMS or MMS. This will work alongside iMessage, which will continue to be the best and most secure messaging experience for Apple users.