Something like 10 years ago I had a similar idea - a 2D shooter with the feel and gameplay of a FPS, only that in my case I thought of making it top-down, and the plan was that visibility would be a huge thing - your 2D character would only see things from their point of view that weren't blocked by the level geometry or other players.
I never completed that game, for various reasons. But in the course of making that prototype, I did a lot of research about the networking model. I read every article I could find about client-side prediction, server reconciliation, and entity interpolation. I didn't want all this effort to go to waste, so I wrote what I had learned in article form, and put it on my website.
That's the never-told-before origin story of my multiplayer networking articles :)
https://gabrielgambetta.com/client-server-game-architecture....