My greatest complaint with the two Zeiss lenses I have used in the past (Planar 50 ZM and Planar 50 ZF -both excellent lenses although I prefered the ZM over the ZF) has to do with the front lens caps which leave a lot to be desired in terms of functionality. If you are shooting fast the lens caps are very fiddly and they often made me worry that I may hit with them the front element. Zeiss needs to address this some time in the future because it is a very real, practical problem.
The focusing distances may or may not be an issue. I have learned to live with the 0.7m min focusing distance of most rangefinder lenses and perhaps I could do the same with 0.9 if I had to. It really depends on your shooting style but any limitation imposed upon you by your equipment certainly cannot be welcome.
Having said that, if someone wants a new Sonnar 50 lens there's only one currently in production, and that's the Zeiss lens. But if you are not specifically after the Sonnar look then the Summilux Asph is a very, very enticing proposition with many users reporting it as the best 50 lens available to humanity, (i.e. with uncompromising performance in every single stop). For the price it better be (and my opinion, relative to what I have used in the past, is that it is).