Why not have a rule that will make newbies account that requested for a loan to be reported and deleted?
Just no more newbie jails that is a theymos' vision and the reality of the forum.
With this post, if theymos' vision does not change, the newbie jail will never return but human always can change, who knows.
Limiting newbie participation is very harmful for a community. Newbie jail will never return: I consider the newbie-jail period to have been extremely damaging to the forum. When barriers to participation are too high, then the best people often just won't go to the trouble of joining, and the people who are willing to jump through the hoops are often people who aren't good for the community: people with nothing better to do, scammers, get-rick-quickers, etc. Having a permanent newbie jail policy would improve things a lot in the short-term, but would end up being a fatal poison to the community.
The low signal-to-noise is a real issue which seriously annoys me and is often on my mind. But as you mention, fixing it non-destructively is difficult.
Scam with loan from newbie, I believe that there is no newbie with loan service here so with experienced users and loan providers, they will not accept any newbie loan request. No chance for newbies to scam experienced loan service providers.