The only problems I have with voice acting is that it sometimes prevents you from naming important characters, and that development costs may rise and make it financially hard to justify sub quests and optional characters because you might spend money on something a significant portion of the players aren't going to experience. However, with the progress there has been in voice synthesising over the past years, this might not be an issue anymore after the current or next gen.
Important characters might get real voice actors, while minor characters all get synthesised voices to cut costs.