We must not forget the following: Either Apple has made a deal behind the scenes with a panel manufacturer to produce new display panels that also support 220PPI at 120Hz, or we still have to wait for such news from the big panel companies.
Since Apple Macs are a small portion of the PC market, I imagine the issues with Mac scaling aren't a major driver of monitor production, and since Windows supports sub pixel anti-aliasing and scales non-optimal size/resolution combo.s substantially better (and thus Windows users don't seem to worry about hitting 'sweet spots' like 5K/27"), I'm following up your post with a question...
How strong is the demand for 5K monitors in general, and 5K at 120-Hz in particular, in the Windows PC community?
From reviews and discussions online, they seem pretty happy with 4K.
Also, it's my understanding the bandwidth demands of 5K at 120-Hz will be high, such that many computers don't have the built-in connectivity to drive such a monitor.
Is there a strong enough demand to justify a major display maker bringing us a 5K 120-Hz display at this time?
If Apple does it, I imagine it'll be very expensive like the ASD. The ASD makes sense if you value high build quality (in a device that sits on your desk, is seldom touched and viewed mainly from the front), excellent in monitor speakers (which can be matched or beaten by non-monitor speakers, and many people have speakers), a web cam (various seen as pretty good to lack luster) with Center Stage (not everyone cares), and you can adjust brightness, etc..., from your keyboard (nice but it is a deal breaker?). And if you don't want to hook it to other devices besides Macs.
