If you're in the US. Starting next year, the Inflation Reduction Act added a $1900 tax credit for purchasing heat pump water heaters so it might pay off earlier than you think.

That depends where the hot water heater is located.

In my case, I was able to get rid of my dehumidifier in the basement and the window unit in the summer. Paid for itself in ~6 months.

Yes. I know of these. Here in the Netherlands those start at about 1000 euro's for a hybrid solution. A full heat pump boiler starts at about 2000 euro's. But you get about 600 euro's subsidy. However, as far as I can tell it will only about half my power consumption for hot water. So with the current electricity prices (about 30ct/kWh) it will pay back itself in about 13 to 15 years or so.

I've also looked at instantaneous water heaters, which could be even more efficient. But those with enough capacity need 400V, which I don't have in my apartment. Also I would probably have legionella growth in my regular water heater if I want to save even more electricity. Which would be a health issue.