Love the idea, but a semi-submerged house comes with huge challenges. The least of which being how to keep the underwater windows clean.
Floating is another matter. In fashion and fully doable. See newspaper Budstikka (NO, but with pics). This house is fully functional, used all-year in a cold climate, with a fire-place and all sorts of clever solutions thanks to the owner/designer (Foss). It can also move around, albeit with limited nautical elegance and range is limited to reasonably sheltered waters.
