Will you have a visitors often (family, friends) and, if so, are there affordable places nearby for them to stay? Do you have any potential boomerang kids or grandkids on the horizon? If so, you might want to plan (for now or the future) how to accommodate them.
Mr Anon-E-Mouse and I are at the early "fantasy" stage of thinking about our retirement home, and whether we might want to live an hour or two outside the city. We've lived in 2 BR apartments in Toronto, Paris and New York City, and now have a 4 BR + full basement house. We love having a small office each and a dedicated guest bedroom, as well as space for exercise equipment and crafts in the basement.
I certainly think we can shrink the size of some our rooms in our retirement dream house, but if we end up outside the city, we're sure we'll want a dedicated guest bedroom for visitors.
Also, having had mobility issues myself (severe back trouble) and having lived with my grandparents, I know I want to have a house that makes one-floor living possible and accommodates people with walkers and wheelchairs.
Maybe you could look at a house plan that you add onto later, for example, a studio wing connected by a walkway to the main house. It could be a source of rental income (Air BnB) as well as a guest / parent / boomerang kid space. Or plan for a garage with an apartment above it in the future?
As for our own offices, if we were starting from scratch, I might design them as a configurable space, with folding doors that could separate them into two spaces or open up into a larger single space.