The first versions of this won't be using it to create characters with plot significance and great depth, they'll be generating infinitely large piles of background character chatter. No matter how big your budget is, you'll never be able to to make a world full of random civilians who don't sound repetitive if every line has to be recorded in advance.
Any prerecorded line having a slight bit of personality to it ("I used to be an adventurer like you, but then I took an arrow to the knee") becomes very noticeable after the first time you've heard it, so the safe thing to do is have lots of the most inane chatter possible ("Nice weather today!") to make it stand out less.
If the game can write new lines and synthesize voices on the fly, you could have more interesting lines without the repetition.
