I agree with the general idea but if we implement this, I'd like to see it in a bit more extended fashion.
We already have the concept of record groups, which allows to split the keyboard into two regions which then get entered into two distinct sets of pattern channels (so what you want can already be partially done with that feature).
It would be nice if this feature could be extended to automatically lock instruments to certain channels (without the keyboard split), and if incoming MIDI data could be filtered as well, e.g. redirect MIDI channel 1 to pattern channel 3, or to instrument 5, or whatever.

Ohh, all my thumbs up for this one!