I'm not an expert on haikus, but I'm guessing that in English, there's an accepted convention that each line in a haiku generally serves as an independent clause?

So:

    What she has given
    them is institutional 
    hagiography

is less "aesthetic" than:

    The story's not clear;
    Durer may have cooked it up
    just to do a nude

One extra layer of machine work could be to use NLP to filter out phrases in which the fifth/seventh syllable doesn't belong to a word that is not a noun. It would be interesting to see how much more it would filter/improve the auto-generated haikus.