I measured the scale of ROTR and the remaining expansion plot from Google Earth but they could be different from the real scale.
The size of ROTR is roughly 13000 sq.m.
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[Remaining Expansion Pads]
[Toy Story Land]
The TSL pad is around 9500 sq.m, big enough for 1 e-ticket but not the scale of ROTR.
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[Tommorwland/Stark Expo]
The Avenger plot is around 10000 sq.m but it may be smaller if the attraction itself only accounts for the space inside the rails (around 8500 sq.m).
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The expansion pad above the Avengers plot could be entered through the Tomorrowland/Stark Expo. The yellow arrow is the possible entrance to the plot. The attraction size could be bigger if needed with the land below it (which I excluded for the land design, roughly a total of 16000 sq.m). This could place a ROTR-scale ride easily.
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It would be great to have TOT in the Avengers Plot and the e-ticket in the larger plot (but I don't think there's enough budget for this). Ocean Park closed their drop tower in 2021. They closed down many major thrilling attractions in the past few years. I think it is good timing to introduce more thrill rides to attract the lost attendance of OP. But the shortcomings would be the sightline and not having the quinjet facade at the centre of Tomorrowland.
[Grizzly Gulch]
This area is enough for ROTR alone without taking out the pavilion (but left with no/ little space for the land). It is big enough to build a proper land with ROTR together with the space of the pavilion.
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They could even expand downwards to the road surrounding the trees and plant the trees below the road. This is a possible expansion pad if they need it. This land gives the most possibility and potential for expansion and I hope they plan it well for future developments before using it.
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Just for reference, BATB is roughly around 8800 sq.m.
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The park still has expansion pads that could hold attractions at the scale of ROTR. For the smaller pads, they could still hold a BATB-scale ride. So there's still space if they want.