Indeed the JEUNE cards were already valid for European destinations before. Now also for Weekend and Senior. What is new are the (quite attractive) cancellation and change fees.

What remains an absolute utter nightmare, including many things that defy any common sense:

• Booking an itinerary for a family where one of the kids has a carte jeune. Impossible. The kid has to be booked separately. PNRs can be "linked", but the youngster won't have access to the same seats in the way he would have when on the same booking as his parents
• To book the Jeune itinerary, one has to select "Young 18-26 years old", even for a child younger than 18. Otherwise the "Does this person have a Jeune card" won't pop up
• Impossible to book an itinerary for two adults with one having a Weekend card and the other one not

There is one thing I don't understand in the article: it mentions that the new cards will be interesting for status customers only after January 2022, I didn't get why.