It actually wasn't WWDC, it was an interview some execs did with John Gruber, which unfortunately was 2 hours long. Segment on visionOS starts here: https://youtu.be/DgLrBSQ6x7E?t=2323

I don't have time to dig in and grab the exact spot, but I'm pretty sure they didn't go into detail much beyond what I said. My guess is text rendering is as good as it can be with state of the art displays, from a software stack standpoint.