I've read the previous threads on it and know that ckemper himself has said he sees no use for it and that he doesn't think steep curves are the way to go about shaping a guitar tone, but I 100% disagree.
I have yet to mix a record where the guitar sounds better without a HPF around 80hz and LPF at around 13khz, usually around 24db/oct steepness. I know tons of live engineers who default to even greater extremes like 120hz/5khz on the desk. Granted I'm speaking primarily in regards to high-gain rhythm guitars in a metal/hardcore setting, but this is something I do regularly and something I have really tried to replicate via the wah hpf (takes two FX blocks just for filters) and the eq low/high shelves turned way down, but when either blind or viewing a frequency analyzer I cannot replicate the same dramatic cutoff on each end that results in what I find to always be a more natural sounding, better fit for the mix, less battling with the vocals guitar tone, despite the unnaturalness of the processing.
That's just one use case - now that you can blend a DI in with the amp feed for a common DI + amp bass rig, why wouldn't you want to be able to hpf the crap out of the amp signal? I very, very frequently run bass tracks through a guitar amp to get a really nasty sounding grit on it, but then filter out below 800hz or so to keep it from muddying up the low end; to be able to do this right in the KPA would be amazing!
There seems to be this kind of "I can't see a legitimate use-case and/or it wasn't designed that way, so your feature request is invalid" mentality around some of requests on here (dly/verb fx before amp block comes to mind) that can be really frustrating as a user. That said, I have 2 very legitimate use-cases outlined here that are both 100% possible in nearly ever other amp simulator at/near/below the KPA's level (AxeFx+Axe2, Eleven, PODxt), and I sincerely hope I'm not alone in thinking this isn't a ridiculous feature to ask for.