[b][u]Melee Weapons:[/u][/b] Eh, I don't have anything against them, but I just don't see how they'd work. Would they be Primary or Special weapons? I definitely don't want a Melee slot; the default subclass meless are perfect.
[b][u]Gun Upgrades:[/u][/b] I agree that there needs to be more player control in gun attachments, at least in terms of sights and magazines. Functional upgrades (suppressors, grenade launchers, etc) are a bit iffy for me. But then, I just don't like suppressors in video games. I also agree that we should be able to apply emblems and shaders to our weapons.
My own suggestion is simply to add more weapon types. Throw in SMGs and automatic pistols as Primary weapons, and maybe light grenade launchers as Special weapons.
What I [b][i]really[/i][/b] want to see is energy weapons in the Primary slot. Something like Halo's plasma weapons would wonderful. At the very least, I want to be able to use the Fallen, Hive, and Vex guns.