Wow, that is beautiful.
Great imagination and craftsmanship.
I have pondered building a big tree house on the back of my acreage. People want to rent tree houses on AirBnB.
The other thing I have considered is building a barn when I retire and put an apartment above it to rent out. I am a pretty good wood worker/finish carpenter.
NH recently passed a law that allows an ADU on every single family home. An Accessory Dwelling Unit. For in law apartments. To increase housing density. If I built something cool I could rent it for $250-300/night.