My response:
Upgrade Lightmapping
Quote: "The current lightmapping just isn't up to snuff anymore, FPSC isn't in v1.0 anymore. Lightmapping needs to fit in with the new and more efficient FPSC! When I add lightmapping to a level it adds a huge amount of memory to the game."
Have you seen the lightmapping in V1.0? If you had then you would know that it has in fact been upgraded.
Scriptable One-Way-Walls and Invisible Walls
Whats wrong with a visible wall, that they cannot pass through? This way, it also stops players from seeing the end of the map.
Multiple Starting Weapons
Did you not just list
how this was possible?
Better OS Support
Really? I mean really? The engine uses Direct X9. It would not be an upgrade of the exiting engine, but the start of a new one that would make this work on different platforms. No Mac, no Linux, no consoles, nothing, without re-coding the entire engine, for that platform.
Increased Maximum Game Memory
If you didn't get what I said above, engine re-coded for different platform. Not going to happen. You can bypass the current limit, but FPSC becomes rather buggy. Why? 2GB is the max memory usage of an application on a 32-bit machine. Or whatever.
Better Camera System
Why do you need more cameras? Its an FPS engine. For making FPS games. You only see one screen, so why would you want another camera?
Memory Test Button
Press Test Game. Read memory usage. Cancel.
Upgraded Fog Effects
Not even an engine change this time, but a DB Pro change. Try using some particles if you want visible fog. The main use of the current fog should be to limit the render distance.
Global Variable Systems
A reasonable request.
Reflection Graphics
The problem with said effect, is that when you look in the mirror you won't see yourself. Why? Because you are an invisible collision sphere and a viewpoint.
Migrate to DarkPhysics
NO! Just NO! DarkPhysics + FPSC + Entities = Low Performance.
Integration of More Engine Mods
One of the problems FPSC has is performance. And you want to bulk it out even more?
Integration of a Skybox Generator and the Entity Workshop
Whats wrong with opening them from the start menu?
Updated Player Voices
Quote: "This can easily be done"
Why don't you do it then? There are other voices available.
Better File Support
Can't you just convert them. And why do you want GIF files anyway?
Patching Support
As with most games in the real world, you either download the patch or use an updater. The game doesn't magically fix itself.
A lot of the other stuff you listed (inventory systems, weather effects, radar, turrets, damage effects) are already possible.
What I'm saying is that there are few reasonable or useful suggestions in this list. Come back down to planet FPSC, a 6 year old game engine that lags like hell.