I've been thinking all weekend that Franco could easily set up Luke with his car being at a deserted Haunted Star however I still don't understand the 'why' unless it is to test Jason by straining his relationship with Sonny. I think it would have been further tested by making the 'hit and runner' Sam but since TG is scheduled for his vacation it was perhaps more convenient for the writers to go this way.
(Heaven forbid their convenient writing give us a cohesive storyline.)
Since we now know that Franco is back on canvas and I'm confident he took Jake the only question is when Jason will know Jake is alive and how it will impact Jason's relationships with Elizabeth and Sam. I think "Jake's Death" is going to be the catalyst that will bring Jason and Elizabeth together (not saying I want that, just saying that I see the potential of this happening as a couple would cleave together to protect their "back from the dead child"). After all, Elizabeth has stated that she feels guilty for keeping Jason from his son and she is the queen of bad decisions/emotional decisions/decisions on the fly. When Jake returns Elizabeth is going to make many emotional decisions.
Jason is thinking 'all heart/no brain' for the first time since his brain injury. Kudos to SB for really showing that transition. It has been a subtle slide ever since Michael was shot and then accelerated somewhat when he was imprisoned but now it is full force. Jason is no longer Stone Cold. He 'may' be able to retain his 'killer status' but he has become very human and it's sweet to see.
It will be curious to see how this ultimately affects how he deals with Franco. He may not be able to pull the trigger when he needs to if his compassion overwhelms his anger and need for revenge. I'm certain that will be the case with Luke (since Luke makes it to vacation, haha)
Sam.. on the other hand, seems more and more distant. Perhaps the blast affected her emotionally and she can pick up where Jason left off. That would actually be fun (twisted but fun).