The house-elf liberation business was embarrassingly underdeveloped even in the books. I can understand the entire wizarding world turning a blind eye to house-elf slavery, and I can see Hermione being the first one to see what's really going on, and sending out a wakeup call. But as it was, she spent the entire series preaching about it and couldn't convince anyone. Not even Harry. Not even most of the house-elves themselves, considering how they all looked down on Dobby. (Ron may be an exception, but his change was so last-minute that he may have just been trying to support or impress Hermione. Anyway, he's just one person.)
I can even see that
working if it becomes a subplot or plot point. I kept waiting for a revelation that house-elves go insane unless they're bound to someone by contract, or they were working off a 400-year racial debt for trying to take over the world. Or something. As it was, they were a truly oppressed race, and Hermione had a righteous cause ... and no one cared enough to give it real attention. Even the author.