Ok - I have an idea that I would like to share. Many feel that The Hobbit has a bit too many multiballs. So here is my suggestion around the mode locks.
I think you can continue to lock the balls (up to 3) for mode locks - BUT in order to qualify the multiball you have to collect all the dwarves at the race (Dwarf, Elf or Man) BEFORE the mode you start.
For example, if you start a mode that requires DWARF to unlock it you must have collected the 4 dwarfs those drops protect. If you have you will get the multiball on mode start - if not you lose those locks and the mode will not add any balls. You would need the 3 at the ELF and 3 and the MAN to get multiballs on those modes.
You can also use color to tie it together (around the dwarfs and mode hex icon). So the dwarves in the bottom left corner would have - let's say - RED lines around the group of dwarves that correspond to the DWARF drops, blue for ELF and green for MAN.
The idea would allow you to both get fewer mutiballs on modes - and allow a fun element of unlocking the multiball to make it more satisfying that just hitting the right ramp to start a mode. And thanks to the book turning feature - you would be wise to start a mode that you have qualified the mode locks for, instead of a mode that you have not.
What about the Gandalf, Bilbo, or Radagast only modes? Then you won't need to collect dwarves for those, and it will use the mode lock as it is now. Also, to make it harder - you can require the player to collect the dwarf first (purple light), and the hit it again (yellow) light to lock it, much like the beast mechs turn yellow to meet the beast mode multiball.