I would say don't bother. The thought is appealing but seriously, people won't use it all that much.
I have built houses with spa.swimming pool and all i did was over capitalised. The new owners had the swimming pool filled in!
My current new Ip has a spa but it just takes up the whole bathroom yet doesn't ever get used. We actually took a dip in the spa and couldn't believe that it took forever to fill up. Then when you turned the jets on, it's so bloody loud, can hardly be called relaxing....more like a fright! MY 2y.o screamed each time we turned the jets on.
and with the water restrictions aswell.
However, I think it's ok f it's japanese style...u know where you wash yourself first then take a dip in it and just leave the water for next use.