Onboard Quest in future mid range Rift
Future versions of the rift will be wireless, with eye tracking and several inside out cameras. With likely need for local tracking for latency and bandwidth reasons, as well as potentially re projection, having all that hardware on the headset itself will significantly simplify the product and lower requirements on the PC side.
But further, it will enable high end rift users access to games on the go like quest users just as quest users have access to high end desktop users. Of course, when running as a standalone, the rift 2 won't have as long of battery and will play at quest frame rates and resolutions. But allowing that platform flexibility really improves customer experience and the hardware flexibility allows new features to be added without higher technical requirements.