I'm thinking something like a team variation of the rambo mode from soldat. It's basically one or two flag ctf (could easily use the old ctf maps), but the flag is a powerful weapon (a raygun or similar item would suit the spytech theme). So the objective is not flag caps, but kills (TDM-style), and the raygun helps because it's super awesome.
Stats would probably also vary depending on the class holding it, because obviously a heavy with a deathgun stands a better chance than a scout with a deathgun.
It could work well, and would promote teamwork to defend the weapon-wielder so the team gets more kills. When the carrier dies, it is dropped just like the flag.
You could spin it numerous ways, like the weapon loses power over time, or the wielder takes more damage, but also deals more. You could probably call it "Prototype" or something along those lines, because it's effectively similar to stealing intelligence.
Sorry if someone said this, because I didn't read the whole thread :3