The obvious move is to extend the French nuclear doctrine to all of the EU and to sharpen the threats. If a single Russian soldier touches EU soil, nuke Moscow.
The same is true of France. If Russia nukes Paris, France will nuke Moscow. If Russia nukes Paris and Marseille, they nuke Moscow and St Petersburg, etc.
The countries that claim to believe that they can use tactical nuclear weapons will probably stop very quickly once people respond to them with approximately equivalent nuclear destruction.
Nuclear weapons are mostly irrelevant, provided that you have them. If you and your opponent have them, what matters is the balance of your conventional forces and your willingness to respond to any nuclear attack proportionally, and to persist in whatever you were doing before.
The French and Russian ideas about deterring non-nuclear attacks etc. are threats, and threats are something to ignore, because the threatened act can always be performed whether or not the demand was met. If someone points a gun at you and tells you to do something you don't want to, why would you do it-- he can shoot you even if you do, so you ignore threats of that sort.
It makes more sense to develop a "Polish bomb" with several other countries cooperating, and share it with the most threatened countries from Finland down to Romania.
It is "just" way more expensive.
I really hope this will finally happen.
The last couple of months have shown that the world is moving back into a multilateral order, in which individual european nations are far too small individually, in which they would be used as pawns on the geopolitical chessboard by nations with far larger economies and populations. i would rather have to discuss the use of defensive materiel with a Frenchman then an American, considering the latter has two oceans between it and any major threats.
There is no European nuclear stockpile, so the first step would have to be making one to safeguard. France has made it clear that its nuclear weapons are France's alone.
It also forces all major nuclear powers to act in some way if it is ever used. It allows france to wield a far larger stick compared to its nuclear arsenal.
It's like better the entire existence of the planet that the other guy is reasonable. I don't like the odds and consequences of that bet.