Apple opens RCS. What does this mean for my Google Messages?

so maybe dumb question: when Apple finally opens up iMessage to the interoperable RCS standard, will my messages from Google Messages be end-to-end encrypted with iPhone users?

Follow up to that: who holds they keys? are they generated on the device, or does apple/google hold them and therefore can decrypt my messages whenever they want?

apple device encrypted end end-to-end generated google google messages imessage iphone keys messages privacy question rcs standard