Here's the pony wall in my bathroom. I built this room from scratch 2 years ago and added it on purpose so that 1) toilet splashes don't end up on the side of the vanity (the wall is tiled, not drywall, so it wipes clean), and 2) so that I can keep everyday toiletries on top of the vanity without them getting knocked off the side onto the floor (on into the toilet!).
If there is not enough square footage for a separate WC, a pony wall can be useful. So IMHO, you can have a pony wall without your bathroom looking dated.
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pony wall
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