It feels like I agreed to work there under one set of circumstances and then the company unilaterally changed the agreement. It qualitatively felt like a bait-and-switch, but that's not quite the right analogy, because the two companies never said that the office situation wouldn't change. I just assumed, and that's on me.
I want to change the dynamic at the next job I take. And I am curious if anyone else here has made some think like that work.
I also definitely wouldn't do that in a situation where I'd be part of a team that shares an office elsewhere. If you do get your private office your coworkers will harbour resentments against you for enjoying a privilege that they themelves do not enjoy and retaliate either consciously or subconsciously by keeping you out of the loop on information that they discuss amongst themselves in their office.
It just seems duplicitous of the two companies that I've been at to verbally say one thing when I still haven't committed and am trying to decide and then do something else 6 months later ... like a bait-and-switch.
Now there are two possibilities. (a) Either they themselves are actually believers in the open plan office kumbaya social happy togetherness crap, in which case they will think you antisocial for not wanting to be part of that. (b) Or, they are fully aware that the company just wanted to save some money on not having walls and the kumbaya social happy togetherness is just the way that they are whitewashing that decision to make it seem desireable to still work there. In that latter case: You not drinking the kool aid will be a red flag to them, making them have doubts about whether they will be able to adequately keep you under control or whether you will turn out to be an unstable element with a mind of its own. They don't need to resolve those doubts. They just need to have them, in order to make them not want to hire you. -- In either case, it's a dangerous game for you to play.
I would only really care about jeopardizing the offer if it's a company that wouldn't have an open office plan, anyways.
The same as if I really cared about any other accommodation (like a salary). I wouldn't trust my salary to a handshake deal.
Edit: I'm not at either of those jobs anymore, but I think if I had tried to negotiate for a shared office after the company had moved to an open office plan, I would have been laughed out of the room.
The point of the stipulation is to filter out toxic companies, so if it puts the job offer in jeopardy, then mission accomplished.
As it is now, my thoughts on the matter are pretty much irrelevant to everyone besides me.