> Do you know if the author or anybody else followed up

I would love to see more recent and similarly thoughtful work on the exact same subject. If I find more, I'll try to remember to come back here and comment. Definitely, I am interested in the clearest evidence regarding whether either paradigm is "actually" more usable, and not just the result of some confounding variable(s).

With a null hypothesis that the classic toolbar is no better than the ribbon, I just wanted to see some data (instead of assuming that what users have now has to be more efficient for those users just because it's what the market-leading product has been giving users for about two decades).