That is a very interesting concept. The parks would almost be empty during the week, which I'm sure means the resorts would cost an insane amount of money. I would only support it if they had solo deals, since I'm not going to pay for two people just to visit the park on my own.
I don't know how deserted they'd be. There are 30,000 rooms on site, which means 100,000 - 120,000 potential guests every day. If you figure the MK gets 40 percent of the guests on a daily basis, and the other parks split 60 percent, that's 40K at the MK, and 25 or so each at the others. Those are party levels. I don't think it would ever be crowded, but I don't think it would be empty enough to make it unjustifiable for them to be open.