Do you think that Zeiss will make a 21mm in between the 18mm and the 25mm ?
Honestly, I'm not sure. I think the 18mm is nice focal length - works great as an ultrawide for FX and still makes a nice 28mm equiv. on DX. 21mm, while great on FX, falls a bit short (or long as the case may be) on DX.
What I'd like to see is something longer than the 100 Makro, perhaps a 135 or even a 180 would be sweet. The ZF range has truly blossomed into a full line-up in a very short amount of time since Photokina 2006. Just a few more lenses should give a completer range from ultrawide to tele.
And of course, it is a Photokina year... who knows what may be announced at the show for Zeiss...
David