I love original themes. I wish that we had more of them. If not that, I'd love to see "sequels" to great themes in the past, kind of like Bride of Pinbot/Jackbot to Pinbot or Revenge From Mars to Attack From Mars. I just know that it's really not all that feasible though.
Even during pinball's best years in the DMD era, it was licenses that ruled the scene. Original themes were still being produced, but they never did as well as licensed games. Now that pinball is only a fraction of what it once was, you have to maximize your potential with each and every release. Using data from IPDB, here's a look at sales results (newer Sterns are left off, because I don't know where to place them). I assume that AC/DC, Metallica, and some others would end up over the 5,000 mark.
Licensed Games
Sales over 20,000: The Addams Family
Sales over 15,000: Terminator 2, Twilight Zone
Sales over 10,000: Indiana Jones, Star Trek: NG, Star Wars
Sales over 5,000: Demolition Man, Bram Stoker's Dracula, World Cup Soccer '94, Creature From the Black Lagoon, Doctor Who, Corvette, Judge Dredd, Jurassic Park, Hook, Last Action Hero,
Pirates of the Caribbean, Lord of the Rings, Simpsons Pinball Party.
Unlicensed Games
Sales over 20,000: None
Sales over 15,000: None
Sales over 10,000: Getaway, Fish Tales
Sales over 5,000: White Water, Road Show, Theatre of Magic
I may be missing a few games. If you have more to add to the list, post it and I'll update the OP. Otherwise, let's just lament the death of original themes.