Mix-down hot water heaters have been a thing since I've been alive (read: any commercial building) - it's not new or strange tech, just find a competent plumber

Mix-down hot water heaters have been a thing since I've been alive (read: any commercial building) - it's not new or strange tech, just find a competent plumber and be willing to pay triple. Or DIY if you're that sort of guy - it's not exceedingly difficult. If I were building a home today I'd "fake" this by simply using a standard tank water heater overspec'ed for my usage, heat that only with solar power on a intermittent basis, and put a tankless water-heater in-line for when/if the temp from the boiler gets too low. I've seen this implemented in more than a handful of higher end new construction myself and it seems like the least hacky/most supportable-by-mortals means of accomplishing it in the typical home.