If I already had an M10 and lenses then it's unlikely I would have bought a Zf. Especially because I could easily carry a film body in a bag and just have both all the time instead of two completely separate setups. The Leica clearly delivers an experience more like using an old camera. With the Zf I have to actively ignore things and I actually turn the screen around at all times unless I need to check a histogram or shoot a weird low angle.
But since I had no recent digital camera, and the M11 has had a lot of issues, I decided to go with the Zf before slamming down my bat credit card (never leave the cave without it, of course).
That said I'm kind of eying an M11 anyway. My main motivation is frankly the size difference specifically of the 50/1.8S vs the 50 Lux ASPH II. However, I find myself mainly just shooting 28mm at the moment, and the Zf and 28mm Z lens is not a huge combo. Additionally, I am baffled by what Leica is doing at 28mm on the M cameras where none of their lenses so obviously outperform the inexpensive 28mm Nikon lens I have to have one, other than the Lux. Unfortunately, I don't want that one due to it simply being too big and I don't need f1.4 on a modern sensor at 28mm. They used to be class leaders at 28mm, and if I look at the SL 28mm it's amazing (though huge). The Nikon 28mm is dirt cheap, light as heck, and a real performer given the price. I do appreciate as a physical object it sucks. As a photographic tool, the value proposition is ludicrous.
Leica still has very compelling options at 21, 35 and 50, but of these, only 50 is a focal length I'm willing to spend that kind of money on (28/50 is an adequate kit for me, I'd just use something else for macro work). For my personal usage, I'd probably prefer the Nikon 20mm f1.8 to the incredible Leica 21,anyway, the Z lens is just incredible and I tend to shoot that focal length on a tripod.
Well, all that aside I think images made with Leicas are certainly very nice, and the M11 is compelling with it's resolution, ISO performance, etc. If my first love was 35mm lenses then this would be much easier due to the 35 APO cron and 35 Lux FLE. If a new 28 is released, my interest would be piqued. At current, it's harder to get as jazzed about spending M11 money and then my best option being a Voigtlander 28mm f2 Ultron II. Props to them and all for making such great lenses but it doesn't quite stir the same feelings in me as Leica and for my main focal length I want a really special world beater lens.