Can you explain why? I haven't been fridge shopping in about 15 years, which probably means that I will have to sooner or later. That style seems more convenient to me, but I also value efficiency.
Much could be saved by using remote compressors but that cost is much higher and usually associated with commercial units.
Maybe one day we’ll have a refrigerant network in a home that refrigeration could tap into, but the cost of specialization will probably exceed the savings :(
Or maybe run a municipal water loop into the fridge? Many are almost there when they have an ice machine (which is also horrible for efficiency).
In winter, you don’t want to bring in very cold stuff from outside the big box into a smaller box inside the big box: the net effect is you’re making the overall big box colder.
Heat pumps are very efficient!
Though your argument holds up if electricity is expensive and heat is cheap (e.g. off grid with woodstove heat)
If anything, you want to bring stuff from outside the big box, put it in the little box to chill further (dumping the heat inside your big box), and then toss out the super chilled stuff from the little box out of the big box.
All in all it's too complicated to work out, but I will admit to leaving frozen goods in the trunk in the winter because of laziness.
But nooooooooooooo, bring the warmish frozen stuff into the little box inside the big box in winter ASAP. (Unless, like I said, you're offgrid with unlimited trees)
If the freezer compartment were above the fridge I'd assume it could mostly rely on gravity.
There is also sometimes a stepper-motor controlled baffle to open/close the link between the two - closed when the freezer is cooling - it usually opens around -18C when freezer temperature is heading lower.
That baffle will also close in frost-free freezers whilst the heater element is melting the ice on the evaporator - it usually reaches +20C and happens several times a week.
Source: https://youtu.be/CGAhWgkKlHI