All right, here's a crazy one which I'm sure could never have happened. What if, after the 1968 legislatives, the FGDS didn't disband, and Mitterrand just got blamed and resigned as he did in rl? Then, they pick a Unifying (hint hint) candidate to represent the non-communist left (though with their grudging support): Michel Rocard or Alain Savary. Preferably the former.
I assume he would've made it to the second round, although I'm also sure he would've lost to Pompidou just as Poher did in otl. But would that make Rocard the new standard-bearer for the left?