The French proposal was intended as an incentive to make nuclear policy evolve and think about common European interests, and wasn't really meant to be practica

The French proposal was intended as an incentive to make nuclear policy evolve and think about common European interests, and wasn't really meant to be practical. As you state, it would require to change German constitutional law. It also reflects France's position as a nuclear power that doesn't partake in US-NATO nuclear planning and sharing (this in turn would be unacceptable to the French political class and public opinion). I think the German acquisition of F-35s is a bit subtle. The Luftwaffe always wanted to buy F-35. I suspect they stalled the subject of the Eurofighter nuclear certification (which would take a good ten years) to force the German government to buy F-35s to keep its commitment to nuclear sharing. The whole thing happened at a time where the ministry of defence seemed disorganized and plagued by scandals. To be coherent with the Eurofighter policy, nuclear certification should have been a top priority ten years ago... The relationship between the German government, the Luftwaffe, the US industry (and Lockheed...) and the German aerospatial industry has always been complex, and Germany has often been keen to use allied programs to avoid internal defense industry problems, with more or less success. See the Starfighter article on Wikipedia for the most egregious example. With the German industry stalling the French-German-Spanish fighter project, I also suspect that they'll plan a similar manoeuver with the Eurofighter replacement.