These are my favorite ideas:
--wainscoting removable wall panels so you can get at the electrical wiring/pipes to do repairs or add/remove outlets without destroying walls
--use standard window sizes to cut down on costs
--orienting house to take advantage of sun--windows and overhangs calculated in such a way that the angle of the sun in summer doesn't enter the house, but when it is lower in the sky in winter, it does enter the home to warm it up. Use of a thermal sink like concrete to heat up during the day and provide passive warmth overnight.
--super insulated envelope
--earth insulation, burying part of the house underground to take advantage of natural soil temperatures keeping the home temperate.
--built-in sauna!
--I love how earthships have an integrated greenhouse that passively heats/cools the house and provides food. I don't know if I would want to go all-in with the earthship idea, but I like the idea of having an attached greenhouse that has a greywater aquaponics system and composting system, so we can harvest fruits and veggies year round.
--use of prefabricated panels (cheaper, more insulated, faster to install, built in a controlled environment)
--metal roof. they are much better these days. Cheapish and last a really long time.
--I'd like to add solar panels or other passive energy converting systems to either cut our bills down or be able to put net energy back into the grid and get paid!
--well thought out layout and travel corridors. Thinking about how you use the home most often--bringing in groceries, it's nice if your kitchen is close to where you park your car/bike. It's nice to have your kitchen open to the living area so you can chat and watch tv while you cook. I like the idea of having half the house be the "public" area and the other half "private", with bedrooms and bathrooms.
--design with accessibility in mind, so you can age in place. Think about when you need assistance getting around with a wheelchair or walker. Wider hallways, pedestal sinks, single story, etc
--focusing on small things you can do to make your house easier to clean/maintain. I really enjoyed this thread:
https://forum.mrmoneymustache.com/ask-a-mustachian/advice-for-making-your-home-interior-easier-to-clean-and-maintain/Basically, I want to design the house in such a way to take advantage of efficient, passive heating/cooling as much as possible, while also focusing on future maintainability (being able to easily fix/update things without having to rip things out) and passively supplementing our normal consumption (food or energy). I also want a house to be easy to live in and not require much upkeep--I want to spend my time on adventures, not cleaning!