Dude welcome to IA. Name 1 change in the last year that wasn't a result of a fringe minorities outcries.
No offence, and I mean it, but all I'm hearing is "it's easier to develop for at the expense of ingame convenience."
Just wayyyyyyyyyy to much shit along with little benefit. To make a campaign you have to
1. Write out the storyboard and see if it will follow the original game by copy or be a completely new story.
2. Make, texture and develop scripts for new models/things that will be unique to help tell the story.
3. Make the map itself and also play test it through alot to ensure there isn't a game breaking pause or crash.
4. To continue the story you'd have to then make multiple maps or have one large massive map (not recommended due to lag depending on how advanced you get and texture loading elements).
5. Get the Hype started and keep up morale to see it through even through it's for a specific audience (Not alot of people play this game as before.. Furthermore alot of people just play online instead).
6. Record new sounds, voice audio and acting depending on how deep you want your story to go and feel. Possibly make cutscenes depending on how detailed you want. Can be skipped to save time but really completes the single player campaign feel.
7. Rally people to help test, build with you and keep it up which is very difficult.
8. A big thing is making the campaign actually playable. The problem with Renegade is the AI just typically runs straight at you.. alot of reviews on Renegade single player said that it was dry, you could tell WestWood had never made an FPS before and the AI was just lackluster compared to other games. This unfortunately is still true as it's just how the game is hardcoded. You can't exactly make this game like F.E.A.R. AI where they could duck. shoot, move to cover and fire behind walls along with communicate with each other. While yes it would be a single player campaign at the end of the day it would just be a reskinned version of the renegade campaign because the AI doesn't and cannot offer anything new. The only thing new you'd be getting is running around to different locations shooting dumb AI in a Soviet Tesla Tank or defending a location from Soviet Rifle Soldiers. While cool in practice and thought despite this handicap it still would be what... You just play the mission and you're done. That's it.
With such a small team compared to the original Westwood studios W3DHub is focusing on the multiplayer because that is where this game really shines.
The closest i've ever seen to a user made campaign would have to be Jerad and his "Colony Z142" something something map. It basically was a port of Halo into Renegade where you had to mount an assault unto a mining facility and do a bunch of shit like fight an end boss and kill aliens. Bear Hunt is also a great example of a single player campaign mission or something that has come close. Join IA and ask for these maps and i'll put them on for you to try if you'd like!