Okay, so here's what ran through my head. If you look at AC3's save data. There is no multiplayer data. Only profile data and campaign save data. If you deleted any data relating to Assassin's Creed 3 from your PS3, what do you think happens to your multiplayer data? It stays with your account. (My friend accidentally/inadvertently tested this.....)
Didn't make sense? Let's keep going. If you got rid of your old falling apart PS3 and got a new one (lets say you went from a PS3 Fat to a Super Slim), without putting any AC3 data on backup or on PS+ Cloud storage, you can log into your account on your new PS3 and still resume multiplayer exactly where you left off on your old Fat PS3. This means your multiplayer data is tied to your PSN account or UPlay (also tied to your account).
Makes sense now? Here's where my theory comes in.
Sony said you will be able to transfer your PSN account from your PS3 to your PS4. And what did we just say comes with your account? Multiplayer data. We also know AC4 will be on both consoles. If you get, lets say..., 3rd prestige in AC4 Multiplayer on your PS3, then transfer your account to the PS4. Theoretically, if there is no changes between the two platforms, multiplayer-wise, you should be able to transfer your PS3 AC4 multiplayer data over to your PS4 copy of AC4. It would make sense, right?
Here's the only thing that might prevent this from working. Save data file types. Every platform uses a different type of save file. So I'm not sure if the PS4 would accept multiplayer data from a PS3 being that it might be a different format.
"Why would anyone care about this?" Well, people like me, who don't want to buy a PS4 instantly will be playing AC4 on their PS3. When I do get a PS4 (and like AC4 with it), it would be wonderful to not have to restart the multiplayer again. (I wouldn't mind starting the campaign over again).
Thoughts?