It would probably help to read about convolution based reverb.My novice understanding is that the reverb block (or any other simulated reverb) is not going to be able to replace the quality of fullrez IR reflections which are "real" in the sense that they are captures of the actual sounds that surrounded the cab at recording. So given this, it does not seem it can be done in a separate block. Was reading through the post you mention but it had turned into such a mud slinging match I never did get to the crux of if/why Jay feels/felt that IR reflections could be as well or better replicated outside of an IR.
it’s all about the length. A short IR is not long enough to characterize a room or space. But a 1024 sample IR is enough to characterize a guitar cabinet.
Since I’m the past we did not have support for real-time convolution of seconds long IRs - then yeah it made sense if you want to provide some room/space simulation to do it through the Reverb block.
Now with this new feature you will have the choice of both reverb through convolution with long length IRs or the tools you already previously had
Since this feature is about supporting much much longer Impulse responses, it makes sense to put it in the blocks that already do convolution (the cab and the IR player blocks). Could it be done in a completely separate block? Yeah it could. Could it be done in the reverb block? Yeah it could. But what does that really change for you? It would just be a different block.
Why does MKI need to “give up something”? Simple, longer IRs take more storage which the MKI version had already partitioned to user IR slots.