If you open a plugin in the Plugin-Host (also in Tracktion!!) the plugins always have the maximum number of IO/Channels. So if a surround-plugin will be used in a stereo-track, more than the half of CPU-Power is wasted (if the plugin has no special detection of zero-channels)
In other hosts (Cubase/Logic) plugins will be opened with number of channels which will be actually used.
I think its necessary to redesign createInstanceFromDescription, to also give the number of preferred I/O Channels to use.
( I now you can change the number of I/O channels of an AudioProcessor with setPlayConfigDetails(), but it in a plugin Host context it makes more sense to set this createInstanceFromDescription, because it nows the maximum channels that can used )