Using the DisneylandForward plots,
Disneyland has roughly 22 acres for easy expansion
DCA has 30 acres for easy expansion
The Toy Story lot plot totals about 125 acres if consuming cheap 1-2 story apartment blocks (apartments are easy to acquire because you're dealing with one landowner and not 100.
Then for something I've never seen mentioned as an expansion area: Angel's stadium. There have been talks of the team being sold or moved, but regardless, even without a move, a theme-park could easily pop-up around the stadium in its 161.5 acre complex. Parking garages coould easily house the demand for the ballpark and a theme park, especially if effort was made to avoid ball-games on the 10ish busiest days of the year. The angels would likely love it, because in theory, people could catch a game for a few hours then hop to the park or vice-versa.
They could easily build a park on the western and southern-end, with a huge shared parking deck on the north eastern end. They could reconfigure the main angel stadium entrance to the north-eastern end, and the amount of ballpark interaction (hotels, restaurants, etc) could be up to both tenants.
To me, a third park at Disneyland seems like a no-brainer, and something that should soon.
With the above plots, they could build massive expansions, two theme parks, and a water park or two (at the Angels stadium or one of the Forever plots) quite easily. The utterly fantastic Volcano Bay is only about 26.5 acres, so they could even fit it in some of the random smaller parcels they own/can aquire.
A water park and third park at Disneyland seem like no brainers that should've happened yesterday, and they clearly have the capacity to build them. DCA would benefit from the DisneylandForward plot more than Disneyland, so if I had to vote, build the Avengers E, build something in the DCA Forever plot, and then have a third park open a couple years later. They have room for more decks north of the existing decks that could account for all lost parking associated with the Forever plots, so honestly, there's not really a single route of expansion in Disneyland that's blocked.