After a few hours of implementing this system in the upcoming release of Instant Impostors.... It's actually slower than simply instancing the object 😅 On a basic tree mesh, 14 seconds with ray portal, 9 with instancing. Oh well, it was worth a try!

One advantage of the impostors is that they have baked-in raytraced AO, as opposed to the hit-or-miss SSAO eevee uses.

Sorry y'all, I've been busy with school and haven't had the time to finish up the upcoming update to Instant Impostors just yet! Hoping to maybe return to it once I get in the swing of things, but right now my time is elsewhere.