During a final season like this, Im all for bringi back unresolved plot lines from the past. We haven't seen or heard about Lumen since she shadily peaced and "moved on", but her MO doesn't fit with the Brain Surgeon's at all.
Lumen was set on avenging herself with a personal vendetta against a bunch of sickos. As I remember it, she left Dexter partially because she was not going to be down with the continued killing. Why would she all of a sudden start surgically scooping brains out as a serial killer, and in Miami no less?