As a compromise, GlissEQ's excellent idea of Export/Overlay can be borrowed. If HarmoniEQ had Export function, and SPAN had Overlay one, then a user would be able to 'see' any HarmoniEQ in a session. Moreover, we could overlay HarmoniEQ's in GlissEQ and both of them in SPAN. It could be another Voxengo's 'thing'. Thus, if some plugin, in future, suppose to have a spectrum analizer, it can be represent by Export button, only.
