The first question how you define "doable". It don't think it would be possible to ride all the rides and see all the shows in one day. The being said, it expected to be slow season you should be able to a good number of the highlights in each park. If you stay onsite or purchase an Express pass you'll be able to get even more done. A good way to describe it would be to try and do DHS and DAK in one day only worse because there are more rides and the number of rides is with longer wait is higher.
Right now, we Escape from Gringotts is a big question mark. The lines for it have been hours long and right now, nobody knows what slow season is going to bring as far as lines go. Also remember show seasons are going to bring shorter hours.