That's a good idea, could you link me to those discussions ?
Here is a link to one discussion on it: @borislavzlatanov/re-jarvie-qozrtj (and it's a part of larger post on the future of communities)
if we were to change the mode to "members only can post" anyone who posted before and isn't a member will see its posts dissapear
Well, that may be desired or undesired behavior depending on who you ask. It may be that we start with the more simple implementation and then add complexity and flexibility over time. Since we are creating completely new things (decentralized communities), it may make sense to develop in small steps anyways, so we can see how it goes and adjust.