That can’t practically be done electronically. Needs to be gas. The power demand is too high for electric water heating

Original comment mentioned £ so they are in the UK. It's possible and not super uncommon to have electric showers in the UK because the 230V provides enough power for water heating unlike the US.

I'm currently investigating options for kitchen sinks and such. It feels quite silly to have a long length of pipe leading from a central source for a small amount of warm water to wash my hands.

Boiling water taps like Quooker and similar are pretty good.

There's a limit: you can fill a medium saucepan with boiling water, but large/industrial-kitchen pans will exhaust the boiling water and you'll need to wait for the next batch.

It's fine for general household use.

Belatedly, no, but I think our installer may have (possibly as a result of the free money!) wildly overspecified the tank which I suspect we will never empty even if we actually tried.

Daikin (and presumably others, but they're the ones we went with) do have integrated tanks/heatpump internal units. It might be worth having a think about your actual needs and it may be that there is a solution.

My experience with electric hot water taps is that they've been universally awful and only a last resort, but equally the state of the art may have moved on since I last looked!