So I will say up front that this idea is probably way too weird to be allowed to live and will almost certainly never ever actually be a part of the game. On the other hand, I have some time to kill while I take my coffee break, so why not? It might interest someone.
There’s a system for PvP combat. How about PvP Diplomacy? Or PvP First Contact? (I thought about posting this in the PvP forum but figured that might not be the right place…)
Here’s what I have in mind: a system in which one person plays their character, as usual, and one person plays the representative of the alien species (or whoever) that is being negotiated with (or contacted). That would get over some of the limitations of scripted encounters and might actually create a challenge.
Basically, both sides would have a set of objectives. To make things interesting, it might be fun to give them a list of things they definitely do not want to happen and a list of things topics/secrets they need to completely avoid. Their interaction could be through interlocking decision trees (you make a decision, then the other side needs to respond in some way based on the choices available), though the Holy Grail here would be to have a more free form discussion. Maybe something where you can type what you want to say. Alternatively, there could be segments that are tied to decision trees and more free form segments, though integrating those two would not be easy.
Rather than having a set number of shield/hull points you don’t want to drop, your goal would be to maximize the likelihood of your government agreeing to whatever deal you reach. There could be two sliders on the screen—one for you and one for the other party—that indicate that likelihood. You’d want to both to get to an acceptable level and would be better off the higher they were (so you want basic agreement, but might get more rewards in the end if both governments were thrilled). In short, you’d want to make decisions and proposals that benefit everyone, while avoiding those outcomes that would annoy your superiors.
There might also be a variety of new powers that would be useful here. For instance, there might be an ability called “Moving Speech.” If you use it, you can make some kind of grand soliloquy, ala Picard, that helps to sway the other side and increases the likelihood that their government would agree to the specific offer you’re making. There might also be a power called “Friends in High Places.” In this case, you may be able to call in a favor from someone you know in the opposing regime. With something like “Making Them Comfortable,” you could be able to find out one of the things that your opponent doesn’t want to reveal, something they let slip.
For Klingons, there could be powers like “Take Hostages” that would influence the outcome of negotiations in various ways.
And, always, everything could devolve into violence. Or a deal might not be possible. Or there could be special twists. Maybe you want to make it look like you’re trying to make an agreement, but you’re real goal is to get the other side to walk away from the table in disgust. Maybe you need to find out what the other side is hiding.
Other than game mechanics, the other big problem would be a que, since I can't imagine a lot of people would want to do this and you'd need people willing to play the aliens.