I believe they're just cosmetic
The guy doing the end of the line video said that the strongboxes were un-related to the end of the line update. He also said that his update is going to be focusing much less on cosmetic items, which leads me to assume they're either working on new weapons, or a new gamemode, or both. Either way, just hold on to your digital hats! A good update is going to show up at some point!
This post fills me with joy.
Squee.