Heck...they not only could do it...they do it NOW.
Let me explain: Epcot...Future World opens at 9:00AM...World Showcase opens at 11:00AM.
Why not open both at the same time? Because until the park fills up, Disney doesn't want guests scattered all over the park so they only allow them into Future World until such time as the park has enough people in it to allow them to go on further into World Showcase. Disney saves money by not staffing WS until later in the day and so guests are forced to stay in one area until Disney decides it's time to open up more attractions for them in World Showcase.
If Disney World attendance is drastically reduced because of a bad economy, I'm sure the Disney people would open parks at their own discretion. Letting 8,000 people run around in 4 differant parks would force Disney to fully staff all 4 parks. Wouldn't it just make more sense to open 3 parks one day and then switch parks the next day. That way even people who only go to Disney for 2 days would still have access to all 4 parks.
I'm not saying this will happen, it was just a rumor I heard from a CM friend of mine. I'm sure it would only be done under extreme circumstances.
I wouldn't like it, but you can't argue that it makes good business sense. Reducing cast member needs yet still allowing visitors access to all parks.