Before I began humidifying my growing area newly potted S/H plants really struggled before new roots made it to the moist zone. With higher humidity the moist zone is higher, and they adapt faster.

I've seen and built similar setups outside in the pond industry, with the seeping rock walls planted and flowing into a pond or basin. I'd use a waterproof backing, silicone or waterfall foam rocks onto the face, using a mix of porous and non-porous rocks. Very do-able.

Google "water wall fountains" and it will give you a lot of ideas for how to construct one.

---------- Post added at 09:02 AM ---------- Previous post was at 09:01 AM ----------

Same here. I eventually set up an area for newly potted to SH plants with a timed mister. It really made the transition a LOT quicker.

Maybe I’ll need a grow-out tank, I’ll think about that.

I hang out on Dendroboard, and they have a few main techniques for creating lightweight sculptural back drops. I have used the Great Stuff technique a few times now, but for this build I’m intending to try the board foam technique. You use layered foam boards, covered in concrete or some kind of waterproof paint. Once done, it can look like very realistic rock, but it isn’t porous at all so I’d have to take that into account.

Here’s an example of one made for an aquarium:
https://www.instructables.com/3D-Aquarium-Background/

I would do mine vertically, with a network of channels for the water to follow and some pockets for larger plants. I want a Nepenthes up by the top, that will need a larger pot. Then have the floating S/H pots right down by the bottom, with some orchids and some cascading plants trailing over the side of the tank. I’m thinking a 20g tank with a 2’ wide x 4’ tall drip wall above it. I suspect that if I run the drip wall in shorter increments frequently, it will mostly water the highest plants (Nepenthes, some lithophytic pinguiculas) whereas running it for an hour once or twice a week will soak everything on the wall, so I can grow plants with a variety of moisture requirements.

Not sure yet whether having the drip wall drip into the tank is a bad idea - if it does I could have it flood the S/H pots which is probably a good thing. Then the tank would need an overflow into a reservoir, and the reservoir would pull water for the drip wall with some kind of filter, which would act as the tank’s filtration system. I would need to do occasional water changes and refresh with RO water.

If the water level in the tank is low enough that the walls can trap some of the humidity around the pots and plants, you'll be unlikely to have sever humidity-gradient issues.

That’s a good point, and while I don’t think I’d like the look of the water level a few inches down in the tank, I could extend the drip wall to have an enclosure for the S/H pots.

So excited about this build! I asked my partner to think of a space in our small house where it would fit, and we can’t think of anywhere, so it may have to wait.

The thing with doing orchids and planted aquariums. Is what is the priority, orchids or the aquarium. The light requirements are completely different for each one. Aquarium plants take much higher light than most orchids take, minus maybe vandas. If the aquarium plants are the priority, then you’ll have to provide some shade for the orchids. It will take a little experimentation to get the light balance right for both.
If orchids are the priority, then set up the aquarium as you would a normal fish tank. You have to remember that orchids like to be wet then dry. Not wet continuously, they need some dry time. If you use the one of the hydroponic techniques, where you bubble the aquarium water and suspend the orchid roots in the mist of bubbles. The roots stay moist, not wet. You will need a few fish on the aquarium or else you’ll only be humidifing the roots , no nutrients.
Good luck with this project, interested in how it goes. Keep us posted and updated with photos.