You cannot evict ppl from floors you own on the spot. Growth is hard to predict.
Hence the dream office will stay a dream unless you are working for a no-growth company doing the same things all the time.
Plus, like already said, you can increase density (at least if the target is not overdensity) in other configurations...
Maybe it's more difficult to over-crowd if you don't have an open-office, but that's a feature, not a bug.
But focussing on how to grow might help. If I stick to the max 30 people rule, I will soon learn that I can do a lot with 30 people.
And if not, why do they have to be so closely integrated? Communication gets hard anyway in such a large group. Why not grow to 40 and then split into 20+20 and make the two teams two separate businesses, with their own office and at the same time reducing the width of the communication channel between the teams.