Is it real wood because it looks like it might be tile that looks like wood.

if is it real Wood than I wouldn't because even though you have a curtain the steam and humidity will penetrate the wood. if you like the look of wood you could always lean a wood towel rack or carving in the shower that way if and when it gets funky you can just toss it out instead of ripping of wall coverings.

Put wood in the guest bath for guests you do not want to stay long.

Q. What happens when the water gets behind the wood and the humidity gets into the wood?

A. Mold. Mildew.

The problem is not whether you can wipe off the surface, it's the jillions of joints that won't be sealed against infiltration and the small spaces that water will get trapped in.

That's why you never see people using it.

It's not in a shower. Of course that would be wrong. It's on the side of a tub. I would think as long as the room is vented properly, it would be ok. I'm not an expert, you might want to talk to a local inspector.

I think you should be asking questions about ventilation. With adequate ventilation you can use anything you want. Even if this was used daily, with over normal ventilation you would be OK. Two Panasonic exhaust fans or the inclusion in your HRV system can avoid any problems.

what about a decking type wood like Ipe? similar to teak, naturally water repellent. ask any boat owner about maintaining their teak though. It's a commitment.

I've seen this done using "exterior" cedar shakes and it was beautiful.

I have quite a bit of teak in my bathroom. Countertops, windowsills, tub deck, etc.

With this not being a wet wall, I'd think you could seal it with a film finish like polyurethane, or if it may see sun and you want to prevent UV issues, use a marine spar urethane. I used a spar urethane on the teak in my bathroom to prevent sunlight from washing out the wood that sees sun during the day.

If you do use a film finish, treat the back of the wood as well as the front. The edges too if you can get to them. That will prevent differential movement and eliminate potential cupping of the boards from the back not being sealed with the front sealed.

You'll likely have to sand after your first coat. Get the urethane on, brush it out, and let it sit. Don't overbrush. You may have some air bubbles, I usually advise to not worry about them. They usually disappear. If you get a significant number of air bubbles, gently but quickly go over the surface with a hair dryer. It'll pop them. When your first coat has cured, lightly sand smooth, and then do a second coat. After that has cured, usually just a light scuff sand is required. Then a third coat. No need to sand after the third coat.

When you sand, use a light touch. You're simply trying to knock down any dust nibs or bits. Vacuum the surface to remove most of the dust and use a tack cloth to remove any residue. If the urethane is pilling instead of coming up as a fine talc-like dust, stop sanding. The urethane hasn't fully cured.

A satin finish might look best versus a gloss.