I think it is worth asking if your contractor can have someone who specializes in plastering specfically refinish the wall. We have a point where new drywall abuts plaster and it's slightly noticable in the right light.

If you have the space, save the door for a future owner.

kats737- thank you for your comments! I'm actually having a plaster specialist come and assess the situation and discuss with my contractor. 'm hoping to install a 12-foot built in bookcase along that wall, so only about 6 inches of the new drywall would be visible, but I agree, I'd like it not to be noticeable. if at all possible. We are planning to keep the door (luckily a small storage unit came with the condo)

What are you planning to do about the millwork along that wall?

Drywall sounds hollow and feels warmer than plaster, and takes paint differently (even after using primer) Generally people don't go around patting walls, unless they are crazy old house people (oh wait... ;)

I'm thinking you would likely be fine with that much breaking up the two finishes; we had to re-install a wall (an archway between LR/DR) and as DIYers definitely couldn't plaster the new section. The wall itself is fine to the eye if you look at each side, but you see the line down the middle where they meet.

Install a bookcase secret door?

We did. Our biggest challenge was getting baseboard to match the rest of the room. we ended up "stealing" it from a pantry cabinet in the back hall. You'd never know today that we took out a door unless you look in the closet on the other side and can see the plywood that was put up first.

Thanks everyone for your comments, very helpful (and reassuring).

Martha- We will only need about 6 inches of baseboard for the small area that won't be covered by the bookcase. I think we'll be able to get an intact piece of existing baseboardfor that.

Lyndee Lee-fortunately lighting won't be an issue. The living room is flooded with light from southern and western exposures with no buildings blocking the light (9th floor). The bedroom will be a little darker, but that will make my husband happy LOL.

kats737-crazy old house person here too!

Elizabeth-the contractor and plaster specialist are going to discuss/make suggestions about the millwork, whether to remove the section that the bookcase will cover, or adapt the bookcase around it. We're not sure just yet.

summersrhythm_z6a-We need space for many more books than a secret door bookcase would give us LOL. My husband is downsizing a library of 10,000 to about 3,000 and I REALLY need this 12-foot run of wall for one of the bookcases we'll have in the apartment.