I'm very interested in this feature in order to create a mixing surface for select inputs and playbacks to a fixed submix for a more tactile experience in live situations where navigating banks and rows of faders could prove too cumbersome, or as a way to automate values of faders without affecting active mute groups like snapshots do.

Perhaps something like the following could work for fader control, as an example: /global/volume/playback/adat/3/spdif/1 [volume] which would set the volume of playback ADAT 3 for the SPDIF 1 submix. In the case of stereo channels, either entry from the pair would be able to control it. e.g. if playback ADAT 3/4 and output SPDIF 1/2 were stereo pairs, then all four permutations of names given by /global/volume/playback/adat/{3,4}/spdif/{1,2} would have the same effect. Ideally, for my use case at least, all input, playback, and output channels should be addressable regardless of the channel layout shown in TotalMix. As a blanket solution, perhaps a toggle could be added to the Options>Settings>OSC>1-4 menus called "expose all channels." If more nuance is desired, then allowing channels to be exposed to OSC controllers but not the mixer/matrix in the Channel Layout menu would be good too. In this case, if a channel is hidden from the OSC controller, it should not re-index the input, output, and playback channels. For example, if ADAT 3/4 is hidden, then TotalMix should simply not respond to commands regarding this channel. adat/5 should always refer to either ADAT 5 or ADAT 5/6, and hiding other channels should not change this.

Of course, I don't have any real knowledge of the technical limitations in TotalMix or the OSC protocol that might make this suggested implementation difficult or impossible, and this implementation might be too narrowly designed for my personal idea for a use case and not work as effectively for general purposes as I imagine. Maybe others have better ideas for an implementation.