Something I've been wondering ever since the PS4 was announced is do all the trophies you've earned on your PS3 become visible on your PS4 trophy collection or do not show up at all? I have been meaning to find out the answer of this for ages :P
I have no idea about these things. But can't you recycle your PSN accound from PS3 to PS4. Cause I thought that your trophies and save data are stored in the cloud of you PSN. So I guess the information is carried over. Maybe if you purchase the game again as a download it will use save data from the cloud.
Again, I have no idea about these things. Just guessing.