I think in the end we need a cross-platform messaging protocol that replaces SMS/MMS that is not reliant on a single app vendor, provides end-to-end encryption and will be supported by mobile network providers.
I can see why Google/Android's pushing for iMessage to be an open standard (they have a page dedicated to this that looks like it's written by a war propaganda writer: https://www.android.com/get-the-message/). It would be nice, but it's also good marketing for iPhones so I fail so see why Apple will play ball unless the likes of the EU implement legislation to make it happen.
Note: I'm not sure the assumption that only the US is dependent on SMS is accurate (I think that it's a standard that works globally and is currently relied on by majority of countries AFAIK).