You could. The only thing is that with slide bar showers, the water outlet is usually low on the wall (roughly waist high), where with no plumbing changes, yours will be up high. With the high outlet, your hose will attach to the outlet up high, then loop down, then back up to the shower head on the bar. You'd want to get as long of a hose that is practical. I can't think of seeing one longer than 7'. I'd recommend getting a 7' long piece of rope or string, tie or tape one end to the nipple up on the wall, and see how much range you get out of the 7' length. With a long hose, one other consideration is the low end of the vertical bar. In a worse-case scenario, if the main bather is short and only used the shower as a body wash, meaning the spray head was normally slid down low on the vertical bar, then I wouldn't want the hose to be so long that it came in contact with the floor tile. You shouldn't have that problem with the outlet up so high. If you go with a vertical bar, I prefer to mount the bar a few inches to the left or right of the water outlet. That allows the long hose to droop in a nice "U"-shape right up and flat against the wall.

Wishenwell, we didn't see a need for a diverter. We've got the hot and cold supplies going to the thermostatic valve, then there are two outputs from there- one goes to a volume control for the rainshower, and one goes to a volume control for the Movario handheld. With that arrangement, we can independently run both showerheads, plus have independent volume control over each. The only thing we can't do is independently set different temperatures, which isn't much of a loss. The diverter systems get pretty complicated if you need to plumb anything other than "one or the other". The other benefit of having the two volume valves, was that it came out less expensive. :-) Hope that helps.

Well for future reference in case anyone ever ends up searching this topic in the future, I did call Kohler today and they did tell me that they use custom hose threads on the wall elbow that only fit their hoses and not those of other manufacturers. It might just be a Kohler thing, as Delta told me their hoses should fit any outlet or showerhead. But it sounds like the faucet guy was right.

I wouldn't worry so much about vertical symmetry, go for a low shower head height and a high shower head height that will work for the people using the shower. Within that range, if you desire you can tweak the height so the fasteners will go through grout instead of tile, that can make the installation easier, plus, years down the road if you change to another shower configuration, it's easier to disguise/patch a small hole in grout easier than a hole in a tile. If you have or want to drill through tile, not a worry. But I'd emphasize functionality before vertical symmetry. As to left/right on the wall, think of how the hose will drape. Hose length will be a big player. My opinion, but segmented metal hoses tend to drape better than plastic, plastic can sometimes pretzel out from the wall a bit.Metal segmented hoses can lay flatter, but the segments can accumulate gunk over time. I prefer metal. You want a "U" drape that will hopefully keep the hose from tangling up with the valve trim every time you raise or lower the head, or take the head off the bracket to spray the far corners of the shower, then replace. Horizontally, I don't know if the existing valve is centered on the wall. It looks to be to the right of center, but that could be the camera angle. Based on what I see, think about mounting the bar to the left of the valve. That would have the head and hose to the left of the valve. The hose will run down the wall and form a "U" then go back up the wall to connect to the wall outlet. The valve will be in the cradle of the "U" in the hose drape. Make the hose long enough so when the head is at its highest, the "U" drape doesn't interfere with the valve, the drape still keeps it clear of the valve. Make the hose short enough so when the head is at its lowest position on the bar the hose doesn't drag on the floor. And ideally, somewhere in that range is a hose length that is long enough so you can also spray down the walls and far corners of the shower for cleaning. That's the Goldilocks hose.