We have a voice actor who regularly writes so why not an animator. Most of them on the commentaries show a good understanding of the show and have funny inputs so why not try to write an episode. It would only count as 30 percent of an episode anyway. And the episode itself would probably be special and different.
It wouldn't be fair for the writers since it probably wouldn't work the other way around. But..whatever
I would personnally love to see an episode written by David Silverman.