Can you request a Release Preview account for both Production and then again for a Sandbox account. We've got an SCA site, and other dev in Sandbox which wont be in Production by the time we ask for a RP account.

I've not seen anyone do that, but wouldn't hurt to ask. I think you'd have to go through your Account Manager though. I'm not aware of any way to do that natively.

You are able to get a Release Preview account for each sandbox. No need to involve your AM, just request the release preview via the form from your sandbox.

TIL!