While such a feature would be useful without doubt, I wonder why it would help you with MIDI export. Pattern channels do not correlate to MIDI channels or MIDI tracks in any way. If you want several instruments to share the same MIDI channel, you should assign them to the same exported MIDI channel. OpenMPT 1.28 will also allow them to be aware of each other (and thus cancel each other's note, as would merging them into a channel do), you can try a test build to verify if this helps you achieving what you want.

Well, here's what i'm working with...

All of my Piano Suites were set up with one PE channel PER NOTE. That is, i would have one channel devoted to say, C-5, and that note was called in that channel only when C-5 needed to be played. This would allow me to simulate the Sustain pedal being pressed, then i could pass a note off '==' in every channel when i was releasing the sustain pedal.

Now i'm using MuseScore to finally create and self-publish the scores to these suites. Instead of re-entering all the notes again, i realized i could just Export the MPTM file into MIDI (now that it's much better supported). Only problem is, to get MuseScore to recognize that all these notes belong on two staves, i have to merge down all the left-hand note-channels to one, and all the right-hand channels to another. Then i can MIDI Export it, and Musescore reads it and notates it perfectly with very little tweaking.

Are you saying there's another way? Or does the FR still need to be implemented to save me time?

I'm actually saying that what you are trying to do is not helping at all - because OpenMPT does not expose its pattern channels in the MIDI file it any way (unless you chose to export in "mapped" mode) - it used to export one MIDI track per pattern channel, but that was long while ago - what it does these days is exporting one MIDI track per instrument. What you need to do is to assign the notes to two different instruments (left / right hand). If MuseScore imports its score per MIDI track, then you are done. If it imports its score per MIDI channel, then you need to assign two different MIDI channels to those two instruments during export. But rearranging your pattern structure is not necessary at all.

Oh Okay! I'll try that! I naturally assumed that each channel would end up with its own staff. (That's right...i didn't actually test it!)

I'll let you know what happens to see if we can discard this FR.

As said initially - I think even if this specific use-case is not a use-case at all, there are still other valid reasons to implement this at some point, so there is no need to close this issue.

OK, now i know why i want the channels to be mergeable.

When exporting to MIDI, all the notes that are still playing in the pattern channels will create notes that stay on thru multiple measures in a score. So you'll end up with notes that are tied over several measures until they're played again.

By combining channels, this will eliminate the notes that are carried over.