Yes, this is the trick. The question / answer cannot be automated, and the registrant must remain in the initial group until the question is answered sufficiently.
One thing I have considered is making the trust-level-2 associate with the additional boards (topics). This way I can use the “received # of likes” as a way of “affirming a correct answer”. This is not ideal, however… it leaves loose ends since anyone can like a person’s answer post, even if the answer is insufficient.
Another thought is to use the API. I use WP as an SSO provider, so I could write an extension that would place a new registrant in the initial group:
If there are no other obvious options, I will go this way.