Let me explain why I don't want a majority of Halo weapons in BL:
If you could download a single add-on, and you only had default ones to start with, would you rather have a gun with a new model that works the exact same, or a gun that does a totally different function, such as making portals? A new feature is going to add a new level of fun to the game, while a new model probably isn't.
That being said, if you can name a Halo weapon that's NOT a generic gun, I'll probably support the idea. I don't care if it's from Halo or not.