6x9 is the same format as 35mm (smaller, but the same ratio). Just buy a Nikon camera, get a Leica R lens w/ an adapter, and use some fine grained film that is developed and printed optimally. I guarantee you won't see a nickel's worth of difference compared to 6x9 unless you want to print really, really big. And if you do want huge prints, you're probably better off using 4x5 and cropping.
I went w/ the Lei-kon combo for years. The Leica Elmarit lens that I owned had very similar IQ to my old Bessa II w/ a Heliar, and looking at prints, it wasn't always that easy to see which one came from which camera. Except that the 35mm camera got shots that I was always missing w/ the red window folder. There is a little difference in neg scans. It's hard to beat bigger real estate for smoothness. But exposure, film selection, and development play such a large role in the final print's appearance, it's essentially a wash.