Update: so far loli frog turned down this idea.
She said that there's no need to add rules, adding rules is exactly what will invite bad actors in and force good people out, and get people to provoke breaking the rules.
According to her, the lack of rules IS the proper way of gatekeeping, because all the bad actors wouldn't want to join an instance without proper rules as they'll consider it to be "unsafe".
So in a way we're already gatekeeping the bad actors out.

And looking at this instance while comparing to many others out there, I think she's right.
The reason why we had no such problems here so far is exactly because we already are an "unsafe" environment from the get go.