Interesting hypothetical (at least I really hope it's hypothetical as I don't want DLP to shrink
The rides that would go untouched without question would be Big Thunder Mountain, Phantom Manor, Pirates of the Carribean, Star Tours and Ratatouille. I would keep Main Street and the area immediately around the castle exactly as it is as well - I like the atmosphere and general feel of the area so wouldn't want to fix something that isn't broken.
Now for the land that I would give away...
My first thought is the Adventure Isle part of Adventureland, including the Robinson family treehouse. Nothing against these specifically. They are nice to walk around, lots of details to look at and enjoy but I feel like once it's been done once in a visit you then just pass through as a shortcut between other rides. Essentially I think it doesn't have the repetition appeal that many other rides do have.
On a similar train of thought, Casey Jr (no pun intended) and the storybook boat area would go as well. Again, nothing wrong with them and I do enjoy the boats in particular but again, it's one of the rides I would only do once but no more than twice in a visit. If I had kids then I may not be saying this as I definitely see the appeal of these rides for families with younger kids especially. Having said that, I'm being ruthless and would get rid of it anyway
In the studios park, the main bit I would get rid of would be the rock 'n' roller coaster area. Not a massive fan of that ride and never really go through that area so feel like it wouldn't be a loss. I know there's been mention of the ride being re-themed but until I've personally seen the end result of that then I would have to keep this on the list as an area to go.
I don't really think there are any other areas I would want to get rid of outside of the ones mentioned already. All other areas have rides that work well within the land, adding to the atmosphere and are enjoyable no matter how many times you go on them. For this hypothetical where land has to go then I thought the areas and rides that have the repetition enjoyment meant they were more valuable to stay.
Don't get me wrong though, I would rather DLP not lose any areas or rides, I love it exactly how it is!
Would love to know if anyone shares my thoughts or has different ideas