You can disable read receipts in RCS just like you can with iMessage: https://www.makeuseof.com/how-to-disable-read-receipts-rcs-a...
Previews are an app feature, not in the RCS protocol itself. I see message previews for SMS/MMS messages on Apple/Android devices despite the SMS/MMS protocol having no concept of previews. Most likely true for RCS as well.
I'm worried about the spam. I hope they provide the ability to turn RCS off altogether if that's going to be a problem.
I don't think they can turn it off altogether, because it's essentially replacing sms, but I hope they allow us to disable a ton of the features or put it into a separate app.
I really don't want spammy users to start seeing read receipts, etc.