Indeed, I had come across that one, except that the idea at first was simply to define the topic without any intention of trying to transform the data. More or less keep the same processing logic but simply provide the ability to specify the topic in order to be able to target the topics imposed by manufacturers.
A relevant solution in my view would be to be able to define the topic « parent » at the device level and specify whether the message content is JSON or flat values (in subtopics). Then for each « feature » of the device define the key of the value, namely the subtopic if the data is flat and the dictionary key if JSON.