No, it has rather obvious technical implications that people like to pretend do not exist. Those features people use are effectively not portable to other platforms short of making iOS run on other people's hardware. Sure, the messaging might be portable, ignoring the security concerns, but iMessage is used for a lot more than that.

In short, any portable version would still be nerfed, just slightly less nerfed than the current situation. The green bubbles would still be there to indicate that their platform can't support core functionality of iOS inside of iMessage.

The green bubbles will remain to coerce people to message IOS users over android as people favor blue over ugly green..

It's a marketing gimmick designed to lock users in using network effects.

These psychological tricks work the best on teenagers and apple have been targeting kids to make them customers for life.

What wouldn't work cross-platform?

Because it has substantive features that don't exist on Android or any other mobile OS. Those features aren't trivial, would be difficult or impossible to replicate, and people use them for serious things.

I don't have a dog in this fight but no one complaining ever really addresses this. iMessage is not just a chat app, even though many people like to pretend it is. It only looks like a chat app if you are not on iOS.