As requested, @fieldOfView, starting a new topic for the possibility of getting a combined/flattened single json file from Cura to use with an updated OctoPrint-Cura plugin.
I wasn't necessarily wanting to add to your workload, but since you are way more familiar with Cura and its inner workings you could probably get a printer settings json export done way faster than I would be able to. The idea is to remove all the inheritance built into Cura's current implementation to be able to upload a single profile file to an OctoPrint plugin similar to the Legacy plugin and a single ini file.
You mentioned potential issues with multiple extruders, and I think there also may be a possible issue with part placement based on some of the stuff I was reading on github as the engine doesn't automatically account for that.
For the later, I think I can handle that from the OctoPrint plugin side, by using the dimensions of the bed from printer profiles and plopping it into the middle of the bed and passing that position to the command line
mesh_position_y parameters. Of course that was an old issue thread I was reading and I haven't yet done any extensive testing on the curaengine and what it's doing today out of the box.