Change to red exposed brick, dark rust coloured stone floor tiles, and stone tub interior and I'm SOLD! Love the floor inset bathtub! Must have comfortable lounger seats in it tho, not public pool hot tub bench style seating.
Here's an indoor Endless Pool with an aquatic treadmill. Imagine this next to an in-ground hot tub, under a sky mural with fiber optic stars, with walls and floors that look like natural stone, rocks, and boulders.