I like all of these but number 2 is most important .

Squaring is so arbitrary why not raise to the 1.75 or 1.50 power?

With active users now shrinking maybe he devs will be open to this. My fear is that they are bizarrely focused on the good post rather than the active users. People can read without joining. If they want users they need to focus on activity. Your solutions would all help (again #2 is easiest fix and would not alter much about the platform.)