Hi Jean-Michel,
I don't know anything about gamification with Papyrus, so I am afraid I can't be of help there. However, I think that the idea of a Papyrus Light is an excellent one and did not realize it was available (my bad). I would seriously consider using it as an option in my SE course in Melbourne.
FWIW, I did use regular Papyrus in one of my SE courses in Sydney a few years ago, but it definitely proved to be unsuitable for beginners (or, even non-beginners). So, I have not recommended it to my students since then, although I mention it, since I give them the option to use the tools of their choosing.
At present, I am recommending NoMagic's CAMEO in my course, which, to me, looks like the best of a bad lot (many of my Master's students are finding even that one challenging to learn and use). MagicDraw's modeling tools are the least user unfriendly modeling tools I've seen (but, far from perfect) and, most importantly, they provide model simulation capability. I firmly believe that model execution is critical for getting students to accept modeling as a valid approach, since it provides them with the thrill of seeing their designs in action. This is something that students are used to and look forward to, from their experiences with programming. Without that capability, it is difficult to get them to be enthusiastic about modeling. They have all heard about agility in software development and model simulation helps support that. Consequently, my suggestion for Papyrus UML Light is that it should add such a capability using MOKA (Light?), possibly combined with Alf.
Cheers... Bran