RCS is not an iMessage replacement though? it's not encrypted, it doesn't support a single identity for multiple devices, it requires cell service and a phone number
RCS supports end to end encryption (it's on by default for Google Messages), Apple just isn't implementing it in their planned implementation of RCS. Google Messages does support a desktop app and you can link it to your phone with a QR code, so it can use a single identity for multiple devices.
I don't mean to insinuate they are like for like. I just mean Apple is starting to pick up scrutiny on interoperability which started with USB-C and I think the focus on this project is going to increase the scrutiny especially if Apple cuts it off.
