If marketers starting picking up the idea, I see "shoot here to win the prize", phone number, email address collecting type of ads promising to "bring facebook back the way it was", "just enter your email address and we'll send you the link!" If you don't think this could work, just remember that a few years back people were installing emoticon packs and CometCursor just so they could have a customized, albeit terrible, experience.
The people who would install a Chrome extension to improve the design of facebook aren't going to be the kind of people who blindly say "ugh, Facebook looks differen, wtf!", and those kinds of people are especially not going to be the kind of people who would write up lots of complicated CSS and JS (both, not just CSS, would be necessary to roll back Facebook's upgrades) to redesign facebook. But this raises a good point: when Facebook rolls out a redesign, do they change the backend enough that an extension that overrode the CSS and JS with the previous design's CSS and JS would break?