Every map will be redesigned in some way, and the length of the game will most likely be doubled from ~12 hours to ~24 hours.
Water Hazard will be more like Valve's pre-release vision, accommodated for the air-boat's floaty physics, and the air-boat itself will have a turbo drive like the buggy
Ravenholm will include the addition of much more difficult zombies, including an additional zombie type you may not know about, as well as some humanoid enemies, though Ravenholm will be dominated by a much more hellish horde.
This mod actually has my attenction. Since I'm looking to create something similiar in future. There will be like restoration of beta assets, like maybe the possible return of the Alien, Combine and Zombie assassins?
Remember when The Simpsons was a good show? Remember that scene when Moe buys a huge deep-fryer from the Navy and says to Homer something like, "I can deep-fry an ox in thirty seconds." Homer's response is "Aww, but I want it, now!"
I'm kind of feeling like Homer about whatever this is you're planning on working on, here.