The picture quality (software resolution quality) will be at least same as in 4k, but with less zoom (distance between display and lenses, less sde, i guess, imho), better displays which means better colors (no shutter glass?!) and less/or no ghosting (kickstarter statement) and no wires on lenses that you can currently notice in 4k version especially when it flashes.
The most important thing about pimax 8k is a high fov and traction system (hope it will be same good as vives, not a nolo thing), both things should affect overall immersion very well even if you run software 2k upscaled to 4k per eye. The software resolution itself isn't a "winner" since it's not really confirmed if it will be possible to run native resolution or not, but you wont find any better solutions on market at this days so regardless what it will be - pimax stays as n1 "high tech" vr headset at this moment
p.s. forum frame doesnt load kickstarter page X_x
p.p.s. the only thing i'm currently afraid off are controllers, they looks pretty different to steam controllers and i guess this will be a problem for some steam games. Even with nolo there were some misunderstandings although they looks and works very similar to vives controllers. Vives controllers are very expensive if you purchase them separately X_x