> I doubt the extra piping and infrastructure is anywhere near worth it

I wonder. Infrastructure investments tend to have absurd payoffs. For example, my solar energy equipment has been generating profit for years.

In my country 5 kW electric showers are common every day items and they add up to a huge chunk of household energy consumption. Switching to a more efficient water heating system has been on my mind for years. If I can use my home server as a heating element, so much the better. Could even use free CPU cycles to mine Monero on it. A solar powered cryptocurrency mining home serving water heating computer. Wow.

I also think a lot about the heat my air conditioners constantly pump out of my house. Seems like a waste to just throw it out of the house like that. Ideally it would be stored so that it could be used to heat other things later... To me it seems like it should be possible with enough integration.

I think it boils down to a) effectively storing heat for later use is extremely difficult to do well, and b) moving heat around properly means 400psi compressor tubes everywhere, and those are a lot more fragile and annoying to work with than regular plumbing, and you need a special gas licence to charge them up afterward.

In contrast to the RV proposal, maybe a better option could be something like a boutique hotel, where you’ve got 100+ showers happening every morning, so having a giant cistern of hot water that you dump all the waste heat from AC, fridges, and freezers into makes a ton of sense.

There are heat-pump water heaters, if that fills in a conceptual gap. The main complaint I've seen with them has just been that they're slow, but that's more of a product-design (at a price point) issue than anything fundamental afaict.