For your situation, I would think a mini electric hot water tank at the endpoint could work as long as you have excess electric, you can dump it there as heat. It's much cheaper storing as heat instead of in battery or ultracap. You'd get losses from leakage, but if it's well insulated it could be worth at least checking out the math.
Ive seen some claims that solar water heating/circulation systems are now more expensive over their lifetime than collecting the solar as electric and heating water, but I've never gone through and sanity checked that calc.
Sounds good but then when that small tank ran out of hot water, I guess there would be a period of cold coming through until the main tank backed it up?
Unless the small tank was big enough for most conceivable uses - in which case, e.g. in the bathroom, it would become a large tank.
A continuous flow unit at least can do what you said in your earlier post, e.g. instantaneously heat up the cold until it starts coming through hot. That's why I was thinking the supercaps, they might provide just enough juice for those 45 seconds or whatever, and also hopefully be reliable enough for decades of use, like you would expect from a hot water appliance.
It would be great if there was some endpoint heater like you describe, that ran from e.g. ultracapacitors that could be trickle charged from solar.
And yeah, having just built our house, I wish I had read this article earlier and learned about using minimally sized piping! Obvious in hindsight.