All I know is that it's limited? Can't read the nihongo either.
The CK100 PRO was meant to be part of ATH's 50th anniversary celebrations, and hence the heavy use of precious (okay, not-so-precious) metals. So far, from what I'm seeing from the design, the IM03 looks similar to the CK100 PRO; it's likely that the drivers were directly transplanted over, except the tube configuration is different now (which honestly affects sound more). The IM02 seems like a slightly tweaked version of the CK90PRO MK2, but the IM01 is a brand-new design with a brand-new driver (I have an idea which one, but can't be sure). It goes without saying that the IM04 is new design. All four models make use of the acoustic horn design carried over from previous models, which is a good thing.
I'd once again like to affirm my deep-rooted admiration for the CK100PRO; it is both ear-piercing and awesome.
Yay acoustic horn! :D Did they ever get the patent for that? You would think that there is plenty of prior art, unless it really is 'non obvious' to shrink it down to that size.