After some consideration, I've decided that if they continue this, I hope that the plot resembles something like this... bear with me as I pretty much sum up the key points from the whole movie:
1) Blake taking time to decide upon taking up the mantle
2) Carmine Falcone (who had to be released in this film) trying to re-establish his family's organized crime but competing against someone new (Penguin, Black Mask, Rupert Thorne, etc.). This new competition wouldn't be seen in the movie, just talked about.
3) A Holiday killer (a la The Long Halloween) begins to kill people affiliated with Falcone and Blake uses his detective skills and a costume to try to learn who Holiday is. Meanwhile, Falcone hires Edward Nygma (doesn't need to be called Riddler) to figure out who Holiday is.
6) Nygma and Blake don't enjoy each other's interference. Nygma realizes Blake is new Batman and figures out that Bruce Wayne was the former Batman. Nygma then learns that Bruce is still alive and hunts him down to determine who the new caped crusader is. He makes several threats towards Bruce and ends up shooting Alfred (who lives). He escapes after his thugs take on Bruce and Selina in their home. This causes Bruce to get into contact with Blake.
7) Nygma holds Gordon's daughter hostage, trying to get Gordon to tell him who the new caped crusader is. Bruce returns and is able to thwart Nygma. Meanwhile, Blake has determined who Holiday will strike next and with Selina's help captures Julian Day.
8) In prison, Nygma offers up that there was a second holiday killer and that he has the information to prove it in exchange for parole. Nygma reveals that Carmine's son was the second holiday killer.
9) Both Bruce and Selina train Blake
10) A final scene where Nygma kills Carmine, and it is revealed that Nygma was working for whoever Carmine's new competition is.
Obviously, those are just my thoughts. But I think Riddler and Holiday would make sense given that Blake was a good detective and that villains work best when they reflect the hero to some degree. I also think making Riddler some type of obsessive PI would make him considerably different from Joker, while I would like to see the mob element return.
The bottom line is that if they continue with John Blake, it needs to be more detective oriented. He doesn't have Bruce's training, and can't be that kind of physical force.