Well, I think Stage 19 suggests that there is a longing to go back to that, even on his part. The condescension doesn't come until the SAZ announcement. Lelouch is completely self-depreciating and even playful with Euphie in Stage 19. That he chooses not to shoot her during the Chinese terrorist incident, something that allows her to figure out who Zero, is indicative that Euphie is somewhat different from the rest of his now-fostered hate for his family. This could be because of how close they were back then. But yeah, her announcement is pretty much a declaration of war to him because he figures SHE KNOWS where he stands right now and she has jeopardized them.
But you do make a good point that he no longer reminiscences on his time as a prince.
Re: Random Observations w/ R2 Spoilers
But you do make a good point that he no longer reminiscences on his time as a prince.