1. I'm extremely short-sighted, and of course I don't wear glasses when I shower, so reading the LCD display to make adjustments was a pain in the ass.
2. There was an option to save settings for guests (which I was) but I never bothered taking the time to use it, so every time I wanted to shower I had to set everything correctly again. Took me like 3 minutes before I could shower. The UI was quite poor, so arguably this could be improved but still...
3. The temperature would reset to the default value if I turned the shower off and didn't turn it back on soon enough. Back to step 2, with the added fun of being covered in shampoo and trying to avoid the cold water drenching me since of course I turned the shower on before realizing it had lost my temperature settings.
Again, the UI for this system was quite poor but still. No matter how good the UI is, the cognitive load compared to traditional system is just too heavy for no good reason.
Just give me a knob for temperature, and a knob for jet strength, like all modern showers. That's all I need.
I trained as an industrial electrician when I was younger so I have some tangentially related experience (though a lot of my apprenticeship was done in a flour mill which is is a very hazardous environment (fuel/air explosions are no joke)).
The conclusion I came to is that while some of the stuff is fairly trivial (constant temperature control for example requires some finesse when you have variable water pressure/flow rates but is solvable) other stuff is actually quite difficult.
How do you handle control inputs?
While waterproof touch screens exist they are ferociously expensive and look more at home in abattoir than a typical shower. So the control would have to be either very simple or controllable from a phone which imposes it's own problems (you would have to run the program before getting in the shower unless you want to take a shower with your £500 iPhone).
In addition there are liabilities (if your software goes rogue and melts the skin of someone that is probably not a good thing).
Safety Standards for showers are rigorous.
Standard for showers are already pretty rigorous (unsurprisingly as they combine electricity in close proximity to water and just for fun throw in scald and slip hazards) so getting a device certified may be expensive.
Integration
The shower would have to be manufactured with the "nest" style controller in it already, modifying an existing shower isn't go to fly as internally there are few standards (except across manufacturers) and anything that impairs the seal is going to get you sued.
None of this stuff is unsolvable if there is a market demand for the product but to be honest I'm not convinced there actually is.
It addresses the problem of wasted hot water when people get involved in other things while they are waiting for the shower to warm up. They turn on the hot water, and then go shave or brush their teeth or start the coffee maker or check email, or whatever, and can waste a lot of hot water between the time the shower has warmed up and the time they return to take their shower.
This gizmo senses when the water has warmed up, and then restricts the flow down to a trickle, until you pull the switch to restore the flow. The change from full flow to trickle acts as a signal to tell you the shower is ready, and the trickle wastes much less how water than the full flow does.
[1] http://www.amazon.com/Evolve-Showerheads-SS-1002CP-SB-Water-...
http://www.us.kohler.com/us/DTV-Custom-Showering-Experience/...
In Japan, water is commonly heated by gas-powered flash heaters. In that apartment, the heater was controlled digitally and there were up/down buttons that would change the temperature by 1 degree Celsius.
It would remember the most recent setting between uses, so all I had to do was remember my favorite number, ensure it was set to that number upon start, and hop in.
It was simpler in function than a Nest and much less pretty, but it was functional and got me the water temperature I wanted.
When the temperature differs from the setup it automatically adjust the "hot" or "cold" temperature to regulate it.
The problem with this is that the whole system would be "reactionary", meaning that temperature regulations would only happen AFTER temperature alterations.
Not sure what "rain brain" is, but their non-electric thermostatic valves do a lot of what you want (we have them in our house).
