Suggested by emoon (and some other people in the past): Provide a libopenmpt interface for rendering each channel separately, e.g. so that you can draw scopes for each pattern channel.
OpenMPT could also benefit from this.
Plugins make this more complicated because if two channels feed their output into one plugin, we cannot tell them apart anymore. Renoise "solves" this by only showing the plugin output on one of the channels (the last one that triggered a note, I think).
We can already render channels to different buffers (e.g. for plugins or reverb), so the infrastructure is there, it just cannot be used to its full extent at the moment.