To get back to the topic,
I now watched the demo video by Paul Davids (https://tinyurl.com/3gckpuar), as well as the one by Pete Thorn (https://tinyurl.com/1j0okjgi).
I also watched snippets from some others.
In order to summarize in particular the Paul Davids video:
KPA vs QC core performance:
He profiles (KPA) and captures (QC) three different amp settings (a Matchless and a Tone King, at the edge of breaking up, and a gainy Matchless setting with two dirt pedals in front), and he says that the Kemper has always more gain than the original, so he has to roll gain down manually to match the profile; the impression I had from the sound bites is consistent with this, the KPA sound had slightly more fizz and less clarity than the original.
What Davids did not mention (at least, I do not remember it) is that the Quad Cortex has always (noticeably) less gain than the original, the was less "chugg" and also a clearly "thinner" tone (less sustain, I guess). This appears also consistent with what others here in the thread reported about other sound snippets from other demo videos.
Furthermore, the original settings (maybe due to the combination with the guitars Davids used, idk) all have some "chimey" high end that neither the KPA nor the QC appear to fully reproduce, imo. Of course, you may tweak these things in manually by EQing the profile/capture, but I guess we are rating the fidelity/quality of the "raw" profiling/capture process, so no EQ is considered here. If I had to choose which out of the KPA and the QC comes closer to the original "chime", I'd probably go for the QC (it seems that the QC would be reaching this chime by staying closer to the completely untreated raw guitar sound, which typically DOES have such a chime, and keeping it by "not fully amping" it, thus less gain).
Performance of other features:
Davids furthermore adds that the reverbs and delays of the QC are below/weaker than the ones of the Kemper (although for the setting where he actually adds reverb, the KPA sound has a weird bubbling in the end that compared to the original simply should not be there, neither does it suit the sound).
In my opinion, the reverbs and delays can be improved with updates. Fwiw, the current reverb and delay sections of the Kemper, which Davids prefers ove the QC, are results of updates (the reverb section has received the crucial update not long ago, when the KPA was already way more than 5 years on the market).
One always has to be wary of the sounds that you get from people who received the unit for review AS AN EXCLUSIVE PRIVILEGE, while that unit is not available on the market yet to the general user. Even criticism is to be taken with its grain of salt.
My conclusions/TL; DR:
But: claims here that it does not sound well or is way below the Kemper in sound quality or whatsoever, just do not seem to be justified. Likewise, the claims about whether or not is is useful at all with its touch screen, and ist knob foot switches and so forth. Some may find it not useful, others won't care, it's just a matter of personal choice for a specific feature that will affect some part of the market, but certainly not the whole general public.
The only issue that might "scare off" a substantial amount of users (imo) could be the mandatory cloud thing (and we might still get a surprise about how little people care about controlling their own data property).
I suspect that the unit's success finally comes down to really putting it in the stores, so that people who are interested can really try it, hear it and feel it.
But that's it, get it in the market for people to test it. Right now, we still seem to be weeks - possibly months away from that point.
