Thats a really hard task to accomplish. Is it poor english stupid? What about foreigners writing in english? Are they all stupid, they won't write 100% proper english. What about misspelled words?
I think irrelevancy and inaccuracy are the best way to distinguish stupid from smart and the key to know what is one what is the other is probably on the subject of the comments and that would be a related/non-related filter not a stupid filter.
Honestly, by the name it got I think it is more intended to get a lot of buzz than to really become a real product. Isn't Mr. Ortiz just trying to get some attention? The definition of stupid is directly related to the reader so you can't have a filter for that, it would have to be personal.