From the resident newbie.... I love speculation, but I couldn't dare read the other thread about this because of potential spoilers. So, this is the thread to muse on only the most recently aired episodes on Showtime. NO info/data from episodes not yet aired. Any episode that has ALREADY AIRED is fair game. As of right now, that would be anything up to and including ep.3 of season 8. As of tomorrow that will include ep.4, season 8... And so on.

Insight:
dexters bloody glass souvenir from Harry's crime-scene "field trip" is a fantastic tie-in with dexters chosen trophy method.

Speculation:
deb reconnects with Quinn as she struggles to come to terms with a new identity as a killer. She also becomes an informal patient of Dr.Vogel, who works to soften her heart toward Dexter, and simultaneously becomes like a mother in dexters heart.
Hannah shows back up in dexters life somehow, in a way that promotes hostility between her and the Morgans, and things steadily escalate.
Quinn somehow becomes abreast of the Morgan's homicidal secrets, but responds with acceptance (perhaps even affection), because, after all, he's had Dexter cover two kills of his own already. Well, one technically, but regardless.... The vicious PIs death was something he would've been implicated in, and he did shoot the club owner of his former Russian squeeze.
Something happens to culminate in dex and deb exploring a romantic or sexual relationship together, Hannah walks in on it or learns of it and attacks dex or deb,possibly in a way that leaves a cliffhanger suggesting she's killed one or both of the Morgan's, which would be followed up by Hannah waking up in dexters kill room. Her executioner, however, is deb.
Dexter is dead or crippled. His last request/plea is for deb to accept vogel as he has. true to that, Debs mentor is Vogel, who has become to deb what Harry was to dex. A possible additional mentor would be dex were he alive but crippled in some way.
Deb is with Quinn, who is either her accomplice or reconciled to the realities a serial killer spouse represents. They raise Harrison as their own while continuing the bay harbor butchers work.
I'm not sure how to tie in the brain surgeon...

Perhaps Vogel is the brain surgeon. If she is, and is killed, I imagine Hannah to be the Culprit, because she was betrayed/scorned by dex and wants to hurt everyone he cares about.

In some weird way, I would love lumen to somehow come back. Perhaps, Vogel realizes dex is more a product of environment and conditioning rather than a natural psychopath, and dex realizes he really can have a normal life. Vogel reconditions him while simultaneously training deb to take his place (as a killer). He and lumen not only raise Harrison but adopt Astor (who seemed to like lumen & came around with dex) and Cody. Dexter promised Astor he would tell her if lumen ever became more than a friend, so that could be a way he reconnects with the step-kids. What would be funny as shit would be if Hannah got over her grudge match with the Morgan's and hooked up with Masuka, I mean, who would see THAT coming!?