On the flip side, there are 5 million more people visiting MK now than a decade ago and almost nothing has been done during that period to add capacity. Honestly, nothing meaningful has been done to add capacity since the early 90's, when attendance was just over half of its current levels.
MK has plenty of wide open spaces to handle the crowds. What it lacks is destinations to draw the crowds out of the wide open spaces, clearing room for the people behind them. Instead the park is saddled with things like SOTMK, Pirate's Adventure, and unnecessary FP+ that leave guests lingering in the walkways, rather than absorbing them into other facilities. Again, DL has comparable attendance and all of its walkways are smaller than their MK equivalents (including Main Street, which is more heavily used due to the ease of parkhopping).
In a way, MK's capacity problems are a microcosm of WDW's capacity problems as a whole. Everybody goes to MK because "it's the thing to do". Everybody watches fireworks in front of the castle because "it's the thing to do". But if there were more things to do (worthwhile attractions, good nighttime show viewing locations, etc.) scattered around, it would ease the burden on any single facility. WDW has gotten to the point where it can't perform regular refurbishments because the parks can't stand to lose the capacity, which is simply pathetic.
Whether Disney does something or not, crowds are going to continue to grow. They can either keep burying their head in the sand and pretending that everything is okay, or they can prepare for the future. For too long, WDW has been run like it's going out of business, and it's reaching its breaking point. If they want to continue to charge premium prices, they need to deliver a premium product; what they have now simply isn't it.