Yes, I think some people adapt the French Press Slipper to this pattern. I don't yet have that pattern, but I thought I might try and figure out on my own how to add the flap.'
I really like this pattern! I have another pair OTN now - my daughter and her roommate have both requested pairs. Such instant gratification! I am a pretty slooooowww knitter, but can manage to get one slipper done (seaming and weaving in of ends included) in an evening. I see making alot of these for Christmas gifts!