Yes. Once formed, the group members would have to distribute as agreed or leave the group. It's an in or out situation. Note that this is not a voting group, it's a reward share group. Votes of members are unrelated and unaffected. Because it has to do with rewards, it does not seem relevant to me what the quality of the post was, except by proxy of affecting the payout. Anything to do with regulating the quality of group members posts (though it sounds not nice to me) or "underperforming" would have to be dealt with person to person.

For example, the group could decide to change the reward distribution proportions every month. All members would have to voluntarily agree to the change, or there'd be a split, the group would probably fall apart.

I briefly mentioned that this could be coordinated automatically when starting the group:

Note that these settings could easily be read from a file or the blockchain for ease of use.

There's no reason it could not be updatable by a similar mechanism.

My opinion is that it would not suit projects like guilds, etc., but would suit projects with a common purpose, or from a common community with a certain ideology of sharing, who were already sure of the quality of each members posts beforehand.

I very lightly touched on the idea that not all posts would have to be "group" posts:

Note that this assumes that all posts must be group posts. Perhaps there could be some additional indicator which marks a post as a group post, but this leads to further complications so I would suggest all posts must be group posts.

However I think it would be impractical to create a system where all members must agree on the quality of a post.

Probably an oversight on my part is whether or not a members contribution to the group should be taken into account. The proposal kind of assumes it would be more or less set by the reward a person is entitled to, like your salary in a company. But it could be implemented that it is also automatically affected by contribution.