with all the different versions of Stock weapons you'd wonder why Valve didn't have them as styles unlocked by items, or in the Botkiller case, badge milestones.
it could've been done like this:
- standard Strange: unlocked by using items found in crates, limited to one specific type of weapon determined by the crate it was in
- Festive style: unlocked by using items found in Naughty Winter crates. limited to a stock weapon
- Botkiller styles: unlocked by MvM badge level milestones. lower level milestone unlocks common (ex. Rust for Operation Oil Spill) Botkiller style for stock weapons, higher level unlocks rarer style (ex. Gold for Operation Steel Trap)
and for items tied to achievements, such as hats or cross-game items (but not craftable items, like the achievement milestone weapons, Haunted Metal Scrap, and the SpaceChem items), why didn't Valve make them Stock quali-- oh wait, Backpack Expander sales. duh!
sorry, had to vent a little