This game has been considered finished for several years and Mav has been focusing on development of his two other games. I have been bugfixing the game since then, but I have been planning to wrap that up as well. The latest bugfixes are packaged as a mod and occasionally updated.
Therefore I don't think voice acting will be added to this game unless someone was feeling very productive and added it as a mod. I can't say for certain whether Mav would be interested in using voice acting in his other games, but my guess would be most likely not.