Could be. it's a very old idea. But have to think about what exactly his words are...because I doubt kid Luffy has any idea about all the seas when he did not leave it...though I would expect some reaction from Sanji..unless it's actually true that Oda stopped giving a shit about All blue and Sanji..and he will only realize it once it's done for him.
Main thing about this plot is...in the end we know all the dreams which they have are not something they are aiming for actively(Like how roger did), but the consequences of plot points which oda is adding..saving this, defeating that etc.
So it is possible his dream is uniting the seas...and by some plot point like say using Ancient weapons,, there will be a chance to do that like breaking reverse mountain...and Luffy will take that decision since it's his dream.
Because in the end, I don't see Uniting all seas, being free to roam around all seas to be something childish or stupid or joke..which was the reactions we got from everyone.
- Luffy can tell someone is there
- Sanji can distinguish gender and hear what they are saying.
This is the second time Sanji has heard something whilst Luffy couldnt...and they were right next to each other. People made excuses for Luffy then. No more excuses. Sanji's base CoO is better than his.