Natural language processing has actually gotten fairly good, but not good enough to recognize and parse any given dialogue you could dream up. I think it is good enough to detect a dialogue option, however. I think it would be nice for a player to have the option to speak their dialogue selection rather than select it with a mouse click. The NLP can detect which dialogue option was selected and the NPC can respond accordingly. Non roleplaying types might enjoy this as well as it will add to the immersion factor, even if you don't want to "act" out the line.
Anything that takes away mouse clicks is going to add immersion to the VR experience. Once a game is designed with NLP you open up gameplay possibilities as well.
Some thoughts:
Initiating dialogue by saying a characters name or keywords such as "excuse me" while looking at the character within a certain proximity.
Triggers for spells and specialized actions.
Taking control of units/characters in RTS by calling out names.
Pulling up menus.
Getting a zombie's attention by shouting "Hey, stink face!" at it.
Whistling to attract the attention of a guard.
Reality check:
Playing a game in this way could be moderately embarassing if you have your wife/husband/girlfriend/parents/whoever are within earshot. Especially if you're trying to sex up an elf.
![Wink ;)](./images/smilies/icon_e_wink.gif)
I have nothing to offer in terms of programming, just wanted to share my thoughts.