I'm certain that the reason channel a, b, c and d shows up as different amp models is because their circuits are different. So when on the real amp you switch channels what you do is that you route the electricity through a different electronic signal path (different gain stages, ...). In the Axe Fx, the amp block covers one complete electronic signal path so when an amp has more channels there is a need to create another amp model because the circuits will be different in each channel. When you add an amp block in the Axe Fx, you load it's circuit into the Axe Fx memory and each circuit covers the complete signal path in the amp. So 4 channels is 4 circuits/signal paths and it would require 4 amp blocks. On a real amp they can save components by using relays (they are the ones with the clicking sound when you change channels on some amps) so you don't have to use 4 x 4 EL34's on a 4 channel 100W amp, but in the Axe Fx, it would likely use as much memory creating an internal switching structure within an amp block like that than to just add another complete amp block and what you're asking for is actually just to add more amp blocks. Creating another virtual layer doesn't change the fact that there would need to be a separate amp block for each channel. Also, you haven't addressed the problem where some amps like the Diezel have separate controls for each channel so it's easy to run channel 1 with the treble dimed and channel 4 with the treble completely rolled off. And on other amps most controls are shared.
Also, in the real world, people accept the amps limitation because for most people carrying another amp just isn't practical. But in our wonderful Axe Fx world, if I like the Diezel vh4 channel 2 and 3 but not 1 and 4, I can just as easily add say a Shiva clean and a Friedman HBE to create my virtual 4 channel dream amp (preset). But if the amp block of a 4 channel amp would load 4 amp blocks in the Axe Fx, that would eat 4 amp blocks worth of resources and would prevent me adding much else to that preset.
Now, I'm all for increased useability (I've posted plenty of times about the virtues of adding an originals page which would only display the controls of the original amp or effect) and channels on an amp would seemingly fall into that category, and maybe it should. The way I would see that would be to on the amp block to add exactly as stated, only having say the Diezel Vh4 as a selectable amp model and on the originals page you could select 1, 2, 3 or 4/A, B, C, D,..., just like in the quoted post. But I don't believe that this would ever be switchable by scenes as this would effectively just load a complete new amp block for each of the 4 channels. And to me this would only make sense if (when
) an "originals" page has been added to the Axe Fx.
