I’m not a developer so my comments are probably not all that worth while. However I had the same question as hmerk.
Based on what you describe it sounds like it might be more appropriate as an extension of the MQTT 2 binding than as a separate binding. The binding currently has support for Homie and Home Assistant which both do automatic discovery of MQTT topics and creates appropriate Things for you. This “feels” like it could be a third type supported by the MQTT binding.
Is this a one time thing or does it need to be frequently? If it’s a one time thing, it seems reasonable and not at all unusual to require those steps be performed manually and used to configure the Things needed.
I do not know if it is possible for bindings to use each other like this in OH 2, but I do know that some stuff that is commonly used, like connections to serial devices, have been pulled out into their own bundles. Perhaps MQTT should be done so as well?