Well I'm not sure AMD have those kinds of resources. It would also be a lot of redundant work. AMD would have told Sony what they're working on, and I don't think Sony would pay for them to do something they're already doing. I can see them asking for AMD to take their architecture in a modified direction given how big a customer they are, and I can see AMD agreeing if the gain is big enough, but such different, divergent paths doesn't seem sensible.
ArtX made the GC GPU. They designed it and then were looking for a customer, which turned out to be Nintendo. Then ATI bought them. Then AMD bought them. It's not really like AMD span off an entire design team to do a new GPU. The 360 was also based on an abandoned PC architecture (R500?), that MS were forward thinking enough to see the merit in. It wasn't a fully bespoke architecture though. Things have only got more complex and expensive since then.
I think AMD can do exclusive features, but the more engineering work they need the bigger the cost and the bigger the impact on whatever else AMD are working on. You can't rule out a radically different version of Navi with custom Sony RT hardware, but I think it's a big ask. Sony asking for some level of customisation seems likely though, and it's also possible that three years ago (or whatever) Sony talked with AMD about the direction of GCN and what they wanted to see.
I just think that the more complex and core the feature or functionality, the less likely it'll be exclusive. I mean, MS work with AMD too and have done for a long time now (14 years and counting), and they've been one of the prime movers in pushing ray tracing into the consumer space. But I don't seem them having some kind of unique hardware ray tracing variant of Navi.
I think it's most likely that if anyone has it, everyone has it. But, you know, I live to be proven wrong.