Wife and I absolutely love our undersink water chiller and instant hot tank. I would have put an RO system, but it would not fit. Of note, I do not think RO water is necessarily good/helpful/beneficial for human consumption, but it would keep the tanks from developing scale and prematurely failing if you have hard water.

I'd seal the house (foam insulation) well and condition the attic space (walk in, of course, not a pull-down). I'd suspend ductwork as much as possible. I'd dedicate a spot up there for an equipment rack and run 2x Cat6 cables to just about every wall in each room (though you could argue one wall per room is probably plenty). I would also have a pair run to each exterior wall (smart lighting, particularly Christmas lighting). I probably wouldn't actually install permanent LED smartlights on the house. It would make it much easier for me to install smart lighting in the yard.

I go back and forth over in-ceiling speakers. They don't compare, sonically, to a good system with towers/bookshelves. But having some music in every room that's easy to control beats the pants off a listening room that you don't walk into (my, unfortunate circumstance)

I have an understairs pantry. The previous owners/builders installed pegboard in the pantry. I have pretty much all of my pots/pans organized on it (lids fit in some pegboard shelves). I don't put stock pots or my few enameled cast iron pieces on it, but it is a fantastic way to organize your coowkare, if the space allows for it.

Likewise, pegboard in a storeroom/garage I'm a fan of. We do quite a bit of decorating and have garland for most major holidays, and it's a pretty great way to organize it (Granted, so is a long 2x4 and a bunch of nails, but I think pegboard looks a lot nicer than that)

I do not have a central vacuum. I am highly considering retrofitting one, and I almost certainly would install one if I were ground-upping. I would make sure to include a garage outlet to vacuum cars/shop, and I would also include the sweep inlet valve/dustpan

We have an office with a decent built-in desk. There is a 'nook' that was actually the perfect size for a second desk. My wife and I are both professionals and enjoy our 'battle stations.' Certainly not on the 'must have' list for most, but if an office is on the list, a 'second desk' area for the other spouse, the household finances/paperwork, the kid doing homework is a pretty neat feature.

A semi-central closet with decent airflow/venting for whatever smart home hubs/router stuff you have to be more central than tucked in a corner. Probably overkill, but somewhat useful. Could replace or be part of the 'attic rack' idea, but pretty hard to have an attic with walk-in doors AND central location.

I'm super annoyed by batteries. So if I were to have a fireplace in a place, I'd build it with plans to have an appropriate low-voltage wire/thermostat to control the fireplace than doing it after-the-fact

Power in the soffit, ideally connected to a switch for christmas lights

Appropriate wire runs/plans for low voltage lighting, including ducking under driveways/gates/sidewalks

ETA:
gas + electric panels near each other, transfer switch installed at the time. I would also have this area near where I would plan for an outdoor kitchen and plumb a gas/water/sewer line to the back patio (or wherever I was planning the outdoor kitchen) even if I weren't planning on building it out

This post was edited on 8/19/23 at 9:37 pm