Just got back from my 2 day summit. Started on the 21st (camped just before Trail Camp) and summited/descended on the 22nd.
No issues with visibility or any more trouble breathing than usual at that altitude.
Regarding footwear. I ended up doing the stretch from the portal to Trail Camp with hiking boots and the rest in running shoes. No microspikes or ice axe though my treking poles were great. Had I carried spikes and an ice axe, I would have happily used them on the long stretch below trail camp and the two smaller stretches near the top of the switchbacks. That said, I felt comfortable assuming the risk with my non-snow gear.
One note on the snow stretch below trail camp. A lot of it is melting off which means that a section of that block of snow might not be able to hold a person's weight for long. We got over it fine on the afternoon of the 22nd though there was a hole opening up on the side which made it look a bit like a bridge. (Sorry, no picture)
