Masterwork Milestones were:
#1 Spider-Man (Classic Hero)
#50 Captain Marvel (Cosmic Hero)
#100 Defenders (Team)
#150 Marvel Team-Up (Team Up)

Along with Black Hero (Black Panther)

All have a different theme. So what themes are still out there?
Marvel Monsters
Dark Hero (Ghost Rider, Moon Knight, etc)
Female Hero (Ms. Marvel, etc)
Villain Spotlight (Dr. Doom)