Perhaps it was an intentional decision, just like it was (as I understand it) a decision not to record sysex data in the sequencer.
Unless we hear from the author of the OS, I am not sure we can know.
I recall there has been confusion by users as to what re-channelize does and perhaps when that feature was implemented, maybe it could have been designed in such a way as to include user mapping and selecting of channels.
So far as I recall, though, re-channelize does what it claims to do.
"No matter what I set 'Rechannelize input' to, it always seems to record incoming midi data from ANY channel into the currently selected track on the Command Station."
I have seen before where people who come from hardware or software that use track and channel differently or who are used to recording multiple tracks at a time have some cognitive inertia to overcome.
As far as a workaround, when you consider the sequencer and the sound module/synth engine as two systems within one box, I am not sure why recording midi data (notes, CCs, etc.) on all channels, but only sending it to some of the channels doesn't work.
I have not found time to test that recently, but I definitely recall having developed patterns where I sent some midi data to the internal synth and other data to external gear. IIRC this was done by using the CHANNEL ASSIGN parameters under pattern edit.
For each of the 16 tracks (T01 -> T16) we can:
(1) Assign the track to: MultiA, MultiB, or any of the 32 midi channels we have (C01A -> C16B), and
(2) Choose to (a) not send the midi data (none), (b) send it only to the internal sound module, (c) send it only to external gear, or (d) send it both internally and externally.
However, if you have a multi channel track, so far as I can see, you cannot choose to filter out certain channels to to send. It sounds like that is a feature that would benefit you in what you are trying to do.
Hope this helps.
Steve
Rechannelize (from the Command Station Addendum for OS 1.31):
"This new screen has been added to the MIDI menu. This feature makes it
easier to record to the internal sequencer using an external keyboard.
Rechannelize Input changes the channel and destination of incoming
MIDI data according to the settings in the Channel Assignment screen.
To record multiple tracks, you simply change the track number and preset.
You don’t have to change the channel number of your external MIDI
controller."
The OS 1.31 Addendum has a number of diagrams which over the years I have found invaluable for understanding how midi data flow has been implemented. I highly recommend them.
Perhaps if the Command Station/P2500 line had continued, we might have seen updates past OS 2.0 and perhaps the OS 2.1 or 2.2 Addendum might have included an Input Channel Filter feature. Not sure if its at Gearslutz, but somewhere there is a wish-list thread I believe for the E-Mu Ultra line of samplers. Not sure if there is a fantasy theme thread for Command Stations.
Personally, I would love to see a new-improved Command Station/P2500 with features from the ultra samplers plus OS feature additions--that maintains reverse compatibility with the ROMPlers and the new features added to the Emulator X line.