Downvoted for the tease aspect - don't do that. Instead, make a post describing the assumptions and premises in concrete terms that lays the foundation for your proposal. Or put the whole thing in an open thread and see what responses you get and what you'd need to expand on before making a top-level post.

not downvoted for the problems I suspect you'll hit. I very much hope you can address them, though:

You say: opinions, the judgment, of the group members, not their personal preferences, but there aren't many individuals who can clearly distinguish among these things. If your mechanism depends on rational participants, it won't work too well for humans.

More importantly, you say that a well-defined group charter is a given. But there is no group with such a thing. Groups tend to have natural-language charters, and members routinely ignore even those.

The obvious answer from this crowd is some kind of prediction market, with the "group charter" being turned into a measurable utility function with which to make the judgments about the success or failure of a policy. If people are restricted to using only money from an equal "allowance", plus whatever they have earned from predictions, over time those who have made more accurate predictions gain the most influence on the outcomes of the decisions.

It seems likely that the optimal solution would, perhaps strongly, depend on details that are not given in your post. The composition and size of the group spring to mind, but there are other factors as well.
Is there any specific type of group that you're thinking of, or do you think that there is a one size fits all solution? The latter seems unlikely unless you are thinking of a meta-strategy for choosing between decision making processes rather than a decision making process.

Different members have different opinions, because they're not perfect reasoners and because their interests don't reliably align with those of the group.

I'm going to channel Margaret Thatcher: there is no such thing as society. That is, there is no such thing as "the group's interests" and attempting to compare the solution you have to the "group's interests" is the wrong question. The real question is, how do you aggregate the opinions of those members?

It seems almost impossible to me that there will be a "universally correct" solution, especially if where to draw group boundaries is part of the problem. If the optimal economic organization is hierachical groups existing in a non-hierarchical ecosystem, then it seems wrong to claim hierarchy is universally correct (when it is terrible applied globally) or that non-hierarchical is universally correct (when it can be terrible applied locally).

Given a group objective function so well defined that only measurement errors and uncertain expectations make choosing the optimum nontrivial, there remains the difficulty of obtaining group members' honest estimation of the outcome distribution of the plans under consideration. Further, you want to do better than just averaging estimates; you want to combine information without double-counting.

When (as in reality) people's actual preference for the group decision isn't exactly the stated group objective, I'm daunted by the difficulty of soliciting their reasons+evidence in such a way that they can't dishonestly push the decision toward their desired outcome.

What was that line in Fight Club?

Narrator: When people think you're dying, they really, really listen to you, instead of just... Marla Singer: - instead of just waiting for their turn to speak?

No matter what anyone says here, I get the feeling you're just waiting for your turn to speak. Why don't you just do it?

Well I came up with an interesting idea a few weeks ago for this very problem.

You get a hypothetical bayesian judge to take each person's opinion as evidence.

I don't know the details, but you might make people do some calibration tests to adjust for overconfidence, stupidity, etc.