Not a shower, but in my newly remodeled bath, I have the same problem at my sink. Low water pressure, combined with low flow appliances makes the wait to get warm water much too long. While the slowness doesn't increase the volume wasted, it is very annoying to always your wash hands in cold water. I have a circulation pump on my shower in another bathroom, but I never turn it on, so I don't want one for this sink. It might save water, but the heat wasted to keep pumping hot water from the water heater to the shower all day long is just too much. If I still worked and always took a shower at the same time of day, I could put it on a timer, but my shower time is variable, so it is too much energy wasted to justify it.
This is the solution I came up with for my new bathroom sink and I think it could work for a shower if a circulation pump is too wasteful for you, too - a portable hot water tank at point of use. It's not an 'on demand' system, but a small tank that keeps water hot (in my case under the sink) so when you turn on the tap you have instant hot water, the hot water from the main tank starts flowing into the tank and by the time you've used all the water from the small tank, the hot water from the large tank has arrived and continues to flow. I'm just getting a 1.5 gallon tank but looks like you can get up to a 6 gallon one that is still quite compact and might fit in a cabinet (I know the smaller one does). I guess it would depend on how long hot water takes to arrive from your main tank and how much gpm flows to your shower. https://www.homedepot.com/s/under%2520sink%2520tank%2520water%2520heaters?NCNI-5
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Transoms, light stained floor, cabinet color, lots of natural light
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