Indeed, at this point it appears to be impossible by construction for there to be any sort of evidence against intelligent design.
Except we can nicely demonstrate the design isn't intelligent. That can't be evaded except by invoking some mysterious, unfathomable intention of the alleged designer. The real tough one to disprove would be 'stupid design' or 'capricious design'. Suppose you had something like the son-god of the gnostics; powerful, but neither intelligent nor particularly benign? I could well see such an entity coming up with the human genome as we know it.
And there is always Q. :-)