I think offering Audio books is the final step in completing an already fantastic publishing company. Audio books although good for the "person on the go" --however, let's not lose the true meaning in which it was invented, to allow the vision impaired the pleasure of "hearing their favorite books."
I say "bring it on."
kindle already offers audio for its books, and several good smart phone readers do as well. So electronicly published books are largely already audio ready.