I suppose you could figure the future sale of real estate into your planning, if you were to look at it holistically and adjust for various expenses, risks, etc. For example, owning real estate for the next 20 years will result in additional living expenses such as RE taxes, insurance, and other maintenance costs, as opposed to owning shares of an S&P500 ETF, which doesn't cost anything but generates income via dividends. I am not sure, however, how you could anticipate the details of a future sale of RE (the timing, the proceeds, the cost of "alternate housing options") accurately enough to figure it into a present-day SWR calculation via FIRECalc.
Fair points on cost of ownership. I'm an experienced owner, have bought and sold property several times now, each time extracting very significant profits, both resi and commercial r.e., so quite adept at anticipating the expenses and friction costs, understanding market dynamics, etc.
As for anticipating the resale value, that's no more difficult (or easy) than anticipating the future return on stocks - so how is it more difficult with r.e.? You tell me where the stock market will be in 20 years and I'll oblige by telling you where r.e. mkt will be. Personally, I think my SWAG on r.e. (in my location) likely to be a lot more accurate than anyone's SWAG on stocks.
And I can generate rental income from r.e. instead of using it or selling it - far more tax efficiently than dividends I should add. I am an experienced landlord so no learning curve on that.
And to your point on FIREcalc, I run it both ways, with and without anticipated proceeds from the sale of r.e. - there is a tab for portfolio changes only you have to enter the net amount after fees, taxes, etc.
So, look, I readily admit that my situation is atypical - the value of my r.e. holdings exceeds conventional cost of housing by an order of magnitude, so there is a high level of confidence that there is excess value. And I have bought carefully with an eye towards preservation of value in location(s) that are (and will likely continue to be) highly sought after by very deep pocketed buyers.
My main point was that one size does not fit all. There are cases where including the value of a home should make some sense. I do feel like r.e. is one of those things that scares folks because they don't understand it too well, so the standard opinion is - don't include it or you'll be sorry.