How would this be any different to creating a global back door in signal, wikr or slack?
If they dug their claws into wikr, they'd have to worry about leaks from every single person involved with wikr on top of all potential leaks from law enforcement personnel.
Also, I suspect it's easier to get the warrants needed to create a sting from the ground up than it is for several different law enforcement agencies around the world to each get separate warrants to access wikr/slack/discord/whatever's data.
Once the data legally exists in a law enforcement database, it is relatively simple bureaucracy to share it with allied organizations.
Never trust an app that neither charges for its use (like Threema), nor takes donations (like Signal Foundation).
Wickr's funding is a huge mystery. Approach with caution.