Too early to know, but at the very least MK is getting an overall capacity boost.
- Cars E-Ticket (1,300-1,600) -> this one concerns me as it's a relatively new ride system and completely outdoor and open to the elements.
- Cars C-Ticket Flat Ride (600-800)
- Villains E-Ticket Coaster (1,400 - 1,850)
- Villains E-Ticket Dark Ride (1,800-2,000) -> as Joe mentions above. Once Avengers open, we can get a good idea of how it'll all work out.
Overall, it's roughly about 5,100-6,250 add'l hourly capacity.
Pair that with some of the other smaller improvements (Buzz, CoP w/ Walt), it should help MK overall tremendously. Especially if Villains gets the dual fireworks show concept like SWGE at DL, I think that's where the land will help the most.
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Edit to Add: Disney isn't wasting time on getting other MK-related projects started. They submitted a permit to expand the queue for the ferry, and I'd imagine that's part of an overall improvement package for the transportation network between TTC & MK. Could imagine that the ferry queue expansion would be required if they expected more use out of the ferry and less stress on the monorail system?
One issue Disney needs to resolve regarding MK is how they can better manage guests arriving for special events (Not So Scary, etc.) as they get more increasingly popular. MK's entrance becomes a bottleneck during events.