Did you use landscape fabric or plastic under the river rock? If you like the formality of the current configuration, select a plant that won't require pruning to fit the location. Here I would consider some sculptural cacti or large-scale succulents to repeat for a stark, modern look, but I can't name plants for your zone. For something a bit more relaxed, why not reconfigure the rocks to suggest a dry stream bed and plant the "banks" with groups of grasses, lilies, or shrubs (again, I'm no help with the plant selection). Maybe add a few larger rocks to help with the structure of the "stream". Is there some reason you couldn't reconfigure the rocks to something less rigid than a tic-tac-toe formation?

If we all liked the same things, it would be a truly boring world. Do you mean you like the small smooth pebbles (rather than larger rocks or stones) -- because if so, you can use that look ... but perhaps not as a construction material. If you truly like the "river rock" or any other non-conventional look, then consider using that look to to decorate rather than to build. If you could find a decorative bowl you truly like, you could fill it with pebbles/rocks and place them in any room in your house -- even more than one room. Does your bath get sunlight? Does your yard get sunlight outside the bath window or elsewhere? The reason I ask about sunlight is that there is now a solar powered water pump that could be put in a bowl or birdbath in the yard ... with small smooth creek/river pebbles below and around it to help hold the solar water pump in place for a water feature for your sunlight room or patio or yard. Sometimes stores -- sometimes even the Dollar Tree-- will sell smooth pebbles for planters/pots and you may find some you like well enough to use for decorative purposes. https://www.google.com/search?q=Solar+water+pump+feature+for+fountain+bird+bath&client=firefox-b-1-d&source=lnms&tbm=isch&sa=X&ved=2ahUKEwj4xtjBtqjqAhUej3IEHdRSChEQ_AUoAnoECA8QBA&biw=1366&bih=654 https://www.google.com/search?q=smooth+pebbles+for+planters+or+water+features&client=firefox-b-1-d&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjF17Xzt6jqAhXlhHIEHa03A0kQ_AUoAnoECAsQBA&biw=1366&bih=654 Let us know what you decide -- do post after pics.

Where I am located, in the Colorado Front Range, river rock mulch is used quite often and we have it in our current place. It is used in a 4’ strip around our homes where nothing is planted, because we have expansive bentonite in our soil and need to keep water away from our foundations. It is used to create a strip around the privacy fences in our neighborhood, which protects the fences. It also is used in swales between homes, sloped for drainage. Yes, a few weeds will take root in the rocks, but they are easy to pull because the landscape fabric keeps the roots from sinking into the ground. It is also commonly used here as mulch in low maintenance planting areas. I consider it low maintenance.

I thought about using this product, but my brick cleaned nicely using TSP and a scrub brush and my fireplace is huge - this would have cost a fortune to do a 10' wide floor to ceiling space. For your river rock it may work beautifully. https://www.amazon.com/CHIMNEYRX-Paint-Fireplace-Cleaner-Gallon/dp/B00CFLE2UQ/ref=asc_df_B00CFLE2UQ/?tag=hyprod-20&linkCode=df0&hvadid=194026055947&hvpos=&hvnetw=g&hvrand=7929818841652711179&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1025011&hvtargid=pla-334814716994&psc=1