Since it is being left up to community vote, and only 2 startups can win, isn't including Pinboard unfair to the other 19 startups? As noted in the previous thread, Pinboard is indeed eligible for YCF by the letter of the law, but including a 7-year old startup with a popular founder doesn't seem to fit the spirit of Apply HN.
In fact, if part of the point of this exercise is legitimizing the use of HN as a sort of decorrelated "wisdom of the crowd" hedge for YC's ordinary selection, then including someone with great odds of doing something impactful with the YCF money is a good thing. YC will profit from it, and HN will have allowed that to happen.
Since none of the other startup ideas posted to Apply HN have especially credible founding teams (not a ding!), there's also something to be said for an Apply HN that tries it both ways, both by surfacing an unknown and also by admitting to YCF a company with an established track record. We can then see what YCF does for both kinds of companies.
And, finally: YC's got more than enough money to casually try this out, and one thing I am certain of is that YCF funding Pinboard via an application Maciej Ceglowski posts for Pinboard on Hacker News is going to bring a little bit of joy to my life. It will be fun to watch, for a lot of us, and that's worth something.