I agree with everything you've said, BUT, I find small tank (10gal or less) electric hot water heaters surprisingly cost-effective options if you are using very

I agree with everything you've said, BUT, I find small tank (10gal or less) electric hot water heaters surprisingly cost-effective options if you are using very low-flow aerators and shower heads (0.5-1.0 GPM). And particularly so if you have a small household where everyone can be taught to hit the button* on the wall to turn-on the hot water 30 min before they want to take a shower. The installation cost is vastly lower than heat-pump based units, they fit in a cabinet under a sink much better, are easier to wire up to an on-demand on/off button, is even cheaper to operate during summer months, etc. Would work even better with a solar thermal panel for preheating the cold water. The button in question being a 30-minute auto-shut-off switch, actually.