I thought it already had lying down mode. That's something I wanted to have in VR from day one. More so now that I'm bedridden. Of course they started adding that right after they stopped improving my Quest 1. And of course there is no way for us to add such a simple feature ourselves.
What would a fully open product look like for you? Is the lynx-r1 good enough? I don't think others are focusing on open source other then a full diy kit.