I don't think they'll expand the toy line at least for Disney because the figures that they have appear in the MGM stunt show. They do sell other Indy merchandise, but as far as action figures go, I don't think they'll add ones from other Indy movies or even other characters from the movie.
And my belief as to why the figures look so bad (apart from Indy, who I think looks pretty good) is because instead of trying to make the figures look like the actors who played them, they went for a more generic look because of the "stunt doubles" who play the characters in the stunt show. I'm referring mostly to Marion here, because she looks nothing like Karen Allen. I think they just went for a generic female look with dark hair and hoped no one would notice.
I do have a friend who was confused however because when we saw the show, the actress who played Marion was blonde. When I saw the action figure and commented on how it looked nothing like Allen, he said "Yeah, she's not even blonde!"
Apparently it's been a while since he's seen the movie.