From the view of Inart only the demand matters, which figure is bringing in more sales, so Merry and Pippin imo are gonna be okay for them if they do them in a 2 pack version and maybe even then wont match the sales of Gandalf/Aragorn etc.
Frodo can sell on his own easily with the Ring and Sting and the Red Book etc. but Sam is a harder question, so maybe they will do here a 2 pack as well, expecting about 1000$ for a Hobbit 2 pack.
Boromir is a better candidate than Merry and Pippin, I can see him happen sooner than the Hobbits (except Frodo).
My bet is if Inart sees the demand after Legolas and Nazgul sell good in numbers then they will either do Gimli or Frodo.
Galadriel/Arwen just cant cope with the popularity of most of the main characters imo. Elrond is a safer option for them.
I cant see Sauron happen at all to be honest, size and price of it is the issue here mostly.
Saruman more likely along the line.
Orcs/Lurtz if they happen then they happen far away in the future.
But in all honesty they will most likely do first the main 9 characters than any other. And we are talking here about long-long years even for the main characters.