I’d want it to have a coupled rangefinder and use 120 film (since I’m not keen on respooling.). Both of those the Mamiya still fits. I believe the Zeiss Super Ikonta does too.
All Super Ikonta models have coupled rangefinder; as far as I know, only the B versions have frame counters; originally, I believe, this was done because in tween-Wars Germany Zeiss couldn't count on their customers being able to get 120 film with a 6x6 framing track. All 120, ever, had 6x9 numbers, so they designed around that. The Super Ikonta A (6x4.5) has dual windows on the 6x9 track, as is common for early 6x4.5 cameras, and the C version (the prototype for the Moskva 3, 4, and 5, as well) used the original 6x9 (Moskva 5 had a 6x6 mask and alternative window on the 6x6 track, but was made from the mid-1950s when that was standard). Another (rather uncommon and fairly expensive) frame-counting 6x6 is the Suzuki Press Van -- the dual format, 6x6 and 35mm version had frame counting from a start mark (no red window offered or needed, and it switched to 36mm frame size in 35mm mode) and coupled RF.
In truth, as a Curmudgeonly Olde Farte I must admit to some skepticism about the added technology of rangefinders and auto-indexing, being it adds complexity and could be just another potential source of problems in mechanical beasties that are fifty/sixty/seventy years old.
A frame counter is much less complex, has fewer and more robust parts than a leaf shutter, and none of the parts need to operate in a few (tens of) milliseconds. Yet we have thousands of leaf shutters from a century ago that still work, within reason. As for RF, the oldest example I have is the Kalart on my Anniversary Speed Graphic, which I've been told is vintage ca. 1938 -- and not only does it still work, I was able to adjust it with just a set of precision screwdrivers to match the lens I mounted on the camera. That RF, the one in my Super Ikonta B (with its very functional frame counter), as well as all my 1950s to 1970s vintage 35mm RF cameras, and the ones on a couple Polaroids I own or have owned, have given no problems. Even in cameras where the leaf shutters don't work, for one reason or another.
I'm a lot less worried about shutters, frame counters, and rangefinders failing than I am about the electronics in more modern cameras.