I suspect you will see a wide diversity in weapons mods, just as we had with Fallout3 but even more extensive this time. Weapons have had a major work-over, and there are new ammo types and weapon mods types built right into the GECK in a way that will be easy to use and add/change weapons and ammo types easily (from JES). I suspect that there will be more controls and variables governing combat, and they also mentioned that there are some new scripting commands as well (probably related to iron sights and other new features). Add in the crafting interface and a new dialogue editor, and I suspect we will see more mods for New Vegas than we did for Fallout 3.
I for one can't wait.

As I will be prevented from playing the game for almost 3 hours after getting home from my local midnight launch, I plan to spend part of that time firing-up the new GECK and tearing into the NewVegas.ESM master file. It will be a perfect way to kill the time, and I can get an understanding of how much of the Fallout 3 assets got transferred from Fo3 to FNV (important for peeps like me who are transferring big work-in-progress mods to NV). Much more will be known on game day, it will be very exciting! :celebration:
Modding will work almost exactly the same way as it did for Fallout3, and we have been told that the NIF file format (the format that the 3D models are stored in) is the same as that we used in Fallout3, which means that all of the custom 3D models and textures we made for our Fallout3 mods are directly transportable to New Vegas without modification - which was GREAT! Because we are still in the GECK and almost everything is the same, its like Christmas in October for the modders. :fallout: