The headset-embedded platform can run on pretty much any modern phone with Android and a USB port. That being said, we still need to ensure the total experience is good (CPU, GPU, display latency, render pipeline, etc). If there's lag or graphical glitches we don't want there to be any confusion that it's coming from us.
This isn't strictly speaking related to our hand tracking, and the VR industry as a whole is constantly optimizing. For that reason at this stage a hard minimum requirement is elusive.