The sad thing is that you don't really need a huge algo change to solve the problem. If we're talking content farms that plug up the rankings, primarily sites that scrape most of their content and have extremely low value (answer sites), you can fix it quickly. There are probably 10-20 of these huge sites that built up a ton of links to their homepage and just churn out garbage pages left and right that clutter up the results. Just takes a manual tweak here and there to see a huge improvement without the risk of a ton of false-positives.
Unfortunately, I don't have a ton of faith in this. They'll target the small time spammers but the ones cradled in VC money that are doing this (we all know who they are) will likely not get touched. I'm sure the next time I run a search for some medical problem I have, I'll still find a worthless answers site on top and 20 other "authority" sites scraping that same content.