The only quick patch I'd want to request before next week's study (Tuesday) is tabstrip coloring. It certainly wouldn't be controversial and it's a recommendation that feels the most baked in. Compared to what we have today, I do think it's more usable. 

Tabstrip color recommendation: move from GG200 to #DEE1E6 (custom color)

I explored a range of colors, back-dropped against varying levels of greyscale (from 10% - 90%), and #DEE1E6 increases contrast from 1.2 to 1.31, keeps the "lightness" of the design, and ensures proper contrast with the unfocused tab titles (4.61). 
 
https://gallery.googleplex.com/projects/MCHbtQVoQ2HCZW9TjXpqhOa9/files/MCHtA7U1iMGr66ZB1AFDLfWxAzW9BL-XRzA

P1 because of the timing in user study, but not the end of the world.