Here are my thoughts on much of the perceived consumer "need" for the capability of two parallel amp models in digital amps.
By the way, I am not saying this applies to JH-2, who states that he actually uses and relies on this set-up for his regular guitar gigs. That's fine. This is mean't for all the other guitarists who claim they need or want it...but have never actually used 2 x tube-based guitar amps simultaneously (in parallel), at any time in their lives.
I think it stems from the fact that, excluding the KPA, every other digital amp modeler has a more-or-less fixed set of "baked-in" amps. The owner of these devices are limited to a relatively small pool of available amp models. Furthermore, even with updates, the owner's of these devices are limited by, and completely reliant upon the manufacturer's decision and selection in amp models. In other words, they do not have the freedom of choice to "pick and choose" from a huge (and ever growing library) of amp models, and various permutations therein.
To get around this limitation, manufacturer's such as Line 6, Fractal Audio (and others) have implemented the ability of running two parallel amp models, by which the owner can blend the models to achieve new tones. Ever since this feature was first made available...a growing number of guitarists have suddenly determined that that such a feature is necessary and essential. Consequently, it has somehow become an expected "standard" feature that any new top-of-the-line hardware should offer.
As an Kemper owner...Bullocks, I say!! Kemper has freed us from the shackles of limited amp models and the tyranny of the hardware manufacture who gets to pick and choose what amps are made available.