I am interested in this idea as well- I am in adelaide- I think our winters are similar to yours.
Reading around it there is a lot of talk of having to remove supers over winter. The fear is of the cluster moving up and the queen freezing. However I am wondering if this is always necessary in more moderate climates with little or no frost- the bees in my mothers hive continued to forage right throughout winter?
We removed the flow super and added it back in spring and that went well. But at the end of winter there were several frames of fully capped honey in the brood box. In hindsight I think we could have just left the super on. Removing it entailed draining it - even though it was 60% full of unripe watery nectar. We froze that and made mead from it and fed some back to the bees in spring.
For my own hives this year I am going to experiment with leaving the flow super on some of them. I think there is some potential for winter honey flows here in adelaide- and even if not I think the bees will manage OK in our climate and won’t abandon the queen. One thing I will do though: is block all upper ventilation and insulate the roof over winter. I will only have bottom ventilation. The idea will be that the heat can rise and keep the super warm- but not too much will be lost through the roof (no chimney affect)- and the ceiling will be the warmer than the lower walls of the hive so water won’t condense on the roof and drip back down. The humid air should flow down the cooler walls and exit/get replaced at the bottom of the hive.