Disney's putting a massive investment into
Disneyland California, while that isn't WDW, it should reduce the stress in the Florida park as fewer people on the West Coast choose Florida over California.
Things it could do to ease the burdens.
1) If the parks are busier ( companies making more money) they will be able to remain open later, spreading the traffic a little.
2) They could do more with Extra Magic Hours. A second park a day with EMH) , making staying on property more of a bonus.
3) Open another water park ( although with Aquatica opening recently there may not be quite as much demand) The water parks are much cheaper (smaller) but with both BB +TL regularly closing due to capacity in the summer last year the demand was there. That would reduce some of the Theme park over crowding.
4) More "special events" like Pirates+Princess,
MNSSHP and Christmas special evenings.
I'll accept that, on the surface, Universals 7 day ticket at under $100 looks a great deal, however there is only really 2 maybe 3 full days worth of entertainment. Disney's 7 day ticket may be more than triple the cost, but provides a full 7 days of entertainment.
I think this spring has been very busy, without being quite as manic as other years due to Easter falling so early. It seems that many school districts have chosen from a wider range of dates for their spring break holidays and as a result there hasn't been any slow times at all since the beginning of March.
As has been said, the parks have a capacity and if they reach those capacities Disney has no choice but to close them. Disney is also a business and has the right that when it is close to reaching capacity it can ( and should) make sure those customers that are staying at Disney resorts have the best opportunity to gain entry to the parks. It is after all some of the reason that those guests pay a premium to stay at a Disney resort.
I believe if Disney uses the "busy parks" issue wisely it can boost it's bottom line by making on property benefits more of a deciding factor in people's choices for where they stay.
P.S. I think Annual pass holders also are allowed in during phase 2 and maybe 3 .