Ours will come from pension, taxable accounts, possibly rental income (and if not, then likely the sale of a rental property), and possibly some dividends, as well as maybe side hustles. If necessary, we will do Roth ladders.
Of all the things I worry about WRT FIRE, this is nowhere on the list, although we wont' be super early retirees (mid 40s at the earliest, but likely later for DH who will want to keep working, not need to).