Have sufficient space to keep suitcases and a few boxes, including enough space for vacuums, toys, a step ladder. A large walk-in cupboard or array of cupboards is more accessible than a loft.
A dedicated storage space for bikes (either private or communal) that is convenient to use every morning or evening, even when you’re running late.
If a house has a garden, deck or roof terrace it should also have a water butt or outdoor tap and an outdoor power socket.
With well insulated homes it becomes possible to simply not use the heating for much of the year, but towels still need to dry, and a warm towel is heaven. So make sure towel rails are on a separate circuit and switch.
Include anchors (or something that can have anchors fixed to it in future) on external walls for fitting clip-on canvas shades over large ground floor windows in summer, for extra shade.
Make space just inside the front door where you can dash in from the rain still wearing muddy boots before removing them, even if pushing a pushchair.
Every house should have at least one space for a desk. This should be located away from the noise and mess of the kitchen, ideally somewhere where you can make zoom calls without being interrupted. Ideally all bedrooms should also be large enough to have a desk as well as a bed.
Walls / floors between (at least) the master bedroom and the rest of the house should be sufficiently soundproof to allow parents to have a conversation, or sex, or an argument without children overhearing, and children to play noisily without waking parents.
Even if the kitchen is not the main dining space, include a space for conversations with drop-in guests over a cup of tea.