Our website member TwBurn just smashed our forum with this great news!
He did managed to use a Wii U and a Switch pro controller to play some CD-i games.
This is still very soon to call it victory, but he made it. The first step as been done, and he can be proud of it!
Using an Arduino PCB known to be very versatile and compatible with almost everything, he created an Arduino Library that support 4 different modes.

His work is available on our Open-Source section.

On our forum, he says:

I’ve created an Arduino Library which can be used to emulate a CD-i controller. Currently it supports four different modes (Relative, Maneuvering, Absolute Coordinate and Absolute Screen). I’m hoping to also add Keyboard support once I can find some documentation on the subject.

I’ve been using this library together with a USB Host Shield to connect some modern controllers (in my case a Wii U and Switch Pro controller) to the CD-i with acceptable to good results, depending on the title used. I’ve included these as examples in the library.

The library can be found on: https://github.com/TwBurn/cdi-controller-library

For future updates I hope to include some more examples (like an USB mouse, keyboard), workout some issues, as well as moving my hardware beyond a prototyping phase so I don’t have random wires running over my desk.

Thank you TwBurn!
Your work will help so many people…