I know it's more complex, I should have said it's probably using a version of Polaris 10. I do doubt Vega though. It's either one or the other and probably can't be a mix, based on complety different core architectures and all.
But since it needs backwards compatibility, Its hard to say if Zen could be emulated for Jaguar, if it did, it would significantly reduce the time it takes for games to come out or if old games even got a patch update. I would suspect bobcat is the most likely culprit but significantly clocked higher, I would hope no less than 3ghz, and hopefully very very high clocked memory.