I have to say. I believe WDW's capacity issues are greatly exaggerated. I just walked through AKL lobby. And it was a ghost town.
It's just Magic Kingdom and DHS. MK is actively unpleasant to visit now, and DHS is just too crowded because there are so few attractions in too small a space - and that contributes to MK's problems as people go to where the rides are. But everywhere else is fine.
All they need to do is apply the same technique they used with Fastpass to spread people out across property, get even crowds at all four parks, and crowds would seem like the 1980s again. But that would require new attractions.