I have mentioned this a number of times but will rgab the opportunity and say it again.Nobody can fix google's algorith, not even Google itself. It's out of their hands, always was, always will be. The past already shows, that their algorithm gets a lot of things wrong and penalized small biz and ranks spam high, you all got examples of that. They are already bad at identifying machines or humans.
Assuming they will go for keyprhases such as Marie Haynes is a writer for example.com...", or "Visit my website at example.com" is simply impossible, for thishappen 99.9% of the guest post authorship tag must include the same keyphrase which i doubt. I find more likely to devalue for example ALL authorship links or even anything with /blog/ in its url, but for that to happen it would mean that 99% of the blogs have the same phrasing which I doubt.
If you are wondering how they will try to minimise that, my pov is that they will take into account a couple things such as 1)frequency of posts, 2) how many of these posts are original content and 3)OBL which to my surprise noone mentions here.
Matt refers to spam sites that are there for link selling purposes. If you follow his tweets and his latest activities you would know he is after the private blog networks advertised on the most popular black hat forum on the internet. What does that mean? that the algorithm cant track them thus he is trying to figure it out manually.
Black Hat SEO is the art of making a machines work to look like it has been done by a lot of humans. Google's job on the other site is to find out who's the human and who's the machine. Google gets better at identifying machines, so the SEO industry gets better at mimicking human behaviour. Guest Blog is an area that got abused but trust me there is a difference having a guest blog on a PR5 site, with unique content and 1-2 links and a total OBL of less than 30 than a guest blog of 500 words with 3 EM ancor links on high competitive keyprhases and roughly 20 comments with link in them. Then again in this case OBL would explode so why would you want a link like that anyway? You lose the value thus wasting money, time and resources.