Mod.io is an unstable, slow, and overcomplicated 3rd party modding site.
There's a chance the game crashes when you want to open a mod, or you wanna subscribe to that mod, etc. People cannot mod models, textures, and sounds, which is kind of disappointing because this kind of modding capability is the only reason others play the older Insurgency game, but "that's just like, my opinion, man!"
It would make sense to not allow modding in PVP servers, BUT PLEASE allow it for Co-op at least!. I assume the reason why they chose Mod.io is so we can use mods on consoles, too, but modding was never part of consoles and no one would even care, plus the console version of the game was delayed a lot and it's unlikely we ever get one.
Please leave Mod.io for your (potential) console releases if you insist on adding modding support for it, and add Steam Workshop for the PC version. It's why Day of Infamy even exists