According to Tom Mison himself, Season 3 will be Devil May Cry'd aka: a Reboot.
Look: Mison hinted to TVLine that Sleepy Hollow would need a dramatic reinvention if it returned for a third season.
"If we do get a third season, it would definitely be a reboot," he teased. "It certainly felt, after watching [the finale], particularly the last 20 minutes of it, it certainly felt like we've acknowledged the show that everyone loved, and we can still do it."
EDIT: ...and now here's one possibility that we all don't want to hear:
No word yet from Goffman but here's something more to ponder about: