Right now the books haven't sold this poorly in over 30 years. Hell even in the dark ages of the late 90s, and before the Morrison reboot, the books sold far better than they're doing right now. It could be because the fanbase has dwindled or it could be because a quite of few x-fans aren't liking what they're seeing and are voting with their wallets.
Can it improve? Yeah of course, but it would take a like world building effort in order to do so and I doubt anything like that will come around soon.
I like it but I hate it that some stories that were expect to sell sucked. Like the Joker issue for example. People buy it cause of a well liked character but it has a mediocre story. Other than that, there are good ones as well and I am enjoying it so far.
I love Dexter but I don't think he could do it. When Joker doesn't want to be found then no one can find him. During Joker's "time off periods" or whatever you want to call them, even Batman has no clue where he is at. Dexter knows how to hunt people because he can predict them based on their actions and personalities. Joker is unpredictable in almost a supernatural way.