See, what Charlie Cox says about Matt's relationship with Karen, plus his elevation to her at the end equals all kind of hints for the next season...
Comics Karen knew about Matt's secret, but then it't common knowledge what she did with that knowledge in the storyline that the general internet consensus is that they are leading up to so... well, we'll see. I know they don;t follow the comics exactly by any means, so I;m hoping for the happy, even though I;m not a fan of Matt/Karen.
Okay, here's what I would predict will happen, if we get more:
I see them going down the Born Again route, simply because they have set it up so perfectly. However, I don't see Karen selling Matt's secret, because although there are hints of a past, I think they sorted that with the thing about her brother in season 2, i.e. she's not an addict, and I think that suddenly making her into one now would be a betrayal of the character that they have built (though having said that, they did it in the comics, it was the 80s. I don't see it now). But Fisk will find it out somehow. Maybe Karen will spill his secret accidentally, or maybe even Foggy will, because how awful would that be? But Fisk will find out, and he will begin to systematically take Matt's life apart. Back in the comic story, Matt had a girlfriend who ended up with Foggy for a while. I wonder whether Karen will take that place. I doubt it, but I wonder. This Foggy is more the one night stand and friends with benefits type though, so maybe not!
I don;t imagine the blowing Matt's house up thing will happen. I think it will be more subtle than that, slowly building into his life unravelling around him. But finally, I think that he will go to Foggy and Karen for help, and I think that together they will either beat Fisk or make him back off, and that the whole thing will make their friendship stronger. I think matt and Karen's relationship will be first weakened and then strengthened by his revelation (though I wish it wouldn't be).
Elektra probably won't return immediately, though it won;t be too long before they start to hint at her presence. I think what she does come back, as a leader of the hand, it will fuck Mat up all over again, but that probably won;t happen next season, like Fisk right now, I think she'll lie in wait.
But we'll see. No word yet on whether a 3rd season will happen...