I had this idea (when shipping was cheaper) about renting heat miners during the Nth hemisphere summer. Sending it to Australia for 3-4 months during our winter.

yea, I thought about this as well. I've hard though that its just such a pain to ship the miners around that no many people do it.
I do wonder though if thats because the current miner hardware isn't really made for it, and now that we have open source hardware we could build miners that are much more rigid and made to be shipped around the world multiple times a year.

Do you think heating miners are worth pursuing in countries or climates that don't really get that cold.

yes, especially for heating water. Even in hot climates you need hot water: Shower, Dishes, Clothes, etc.
Obviously it will not that much heat than if you try to heat a house in a cold climate, but thats where open source is so important: being able to build a system that is made for the specific usecase.

Also in hotter climates you usually have a lot more sun and therefore also solar panels and with that free energy, which can be used again to heat water or just heat the air which will usually give you more money back than selling the energy back to the grid