Renoise does not like my Launchpad MK2...

No, so far nothing has been done to support the LP MKII.

But if you could manage to describe the device in terms of a control-map file, that would be really useful

(a control-map is a layoutof the messages that the device can send)

For reference, you can check out the control-map for the classicLaunchpad:

https://raw.githubusercontent.com/renoise/xrnx/master/Tools/com.renoise.Duplex.xrnx/Duplex/Controllers/Launchpad/Controlmaps/Launchpad.xml

Having a description of the LPMKII should make Duplex applications able to run on the device, even if the colors are a bit wrong.

Take a copy of the whole /controllers/Launchpad folder to begin and use it as a starting point?

Perhaps getting rid of all device configuration but one - you can use them as starting points but they all need a unique name (as defined inside the file)

More tips on editing Duplex files here:https://forum.renoise.com/t/how-to-start-editing-duplex-files/30979

Later, I could create a basic driver for the controller - to support the RBG LEDs. Next week or so.