Funny how I see people saying there will be so many different mods and these are the only three I ever see mentioned. I think people are going to end up being disappointed when they can only keep modding their guns with the same handful of mods over and over.
There's many different mods - besides the obvious scope/silencer/e-mag, there's also weapon specific kits like the little boy (reduces fatman weight) and some sort of laser rifle mod. I believe the plasma caster has a turbo mod as well, based on one of the many video interviews. Basically, I expect there to be plenty of mods.
Besides, if the mod framework is there, we can always just mod in more weapons mods to our little hearts' content. Which leaves the console players out in the cold... But that's the way things are.