I have maple breadboard as my kitchen backsplash. It's 11 years old and has held up very well. It's exposed to steam while cooking but I've never had a problem. Just make sure you have a powerful exhaust fan in the bathroom to prevent moisture from accumulating on the walls.

Natural stone, ie: mosaics, tile, or full piece natural stone

I have a tiny bathroom with no window that is used regularly for showers and a lot of steam and humidity is created. Aside from using the exhaust fan regularly, the door is always kept wide open when the bathroom is not being used. Although the bead board is primed by the manufacturer, I applied a coat of Kilz primer (mold/mildew resistant) and two coats of oil base paint. All edges and seams are caulked. It's been a few years, no problems.

I am installing bead board wainscoting for another bathroom. This time using Benjamin Moore Bath & Spa paint in satin finish, instead of oil base paint.

Thanks for your input Well, we wound up using the primed bead board. The wood is pine. We used a Behr Interior semi-gloss enamel which was a paint and primer in one. It's finish is mildew resistant, and it is recommended for high moisture areas. It's also been caulked on all sides. Hopefully it will work well.

Sounds like you did everything right. That should work.