Announcers
A while back when .wpk and .bnk files were available we could replace them with custom announcer files. This would replace the in-game announcer with a custom one. I personally miss having GlaDos insult me when I die.
I have been informed that such files were removed as it created issues when people modified them. However, during some events there is an option to choose between the temporary announcer and the vanilla one. If we had a folder where we could drop the custom announcer files then when in-game choose which announcer we wanted based on the folder name, I think that would be pretty cool.