I Think the Gap is currently filled with a Third person shooter also offers a FPS mode - It’s called PUBG. in case you have been under a rock or something.
That doesn’t mean you have not got something different in mind but there is surely no huge Gap in the market.
I am always keen to work with Shooter fans but Third Person to me is not a true Shooter. It is for people or kids who are not skilled enough in FP modes, they need to use the camera views to peak over and around objects… I can’t stand third person shooters.
But if you have no luck with your project and end up considering joining a Team working on a playable FPS prototype then come have a chat.
All best.