I think the challenge comes in finding the balance point between maintaining the quality of the mainlist and not scaring off new members by annihilating their entries. I think the key to this is stressing that there is no compulsion to write an SCP. When a real shocker appears on the list I always check the member details, and most of the time the user posted their article within half a day of being accepted. There are a few ways I think that this could be prevented:
1) We have a cooldown period whereby a user doesn't get posting privileges until they've been a member for a set period of time (This would be difficult to maintain on Wikidot, I imagine)
2) We have a mandatory sandbox stage for first posters (I know this isn't popular, but I definitely feel I benefited from using the sandbox for my first SCP)
3) A system whereby the new members get given a short and punchy introductory message, i.e. "Welcome to the site, please read these docs before you do anything else, you are under no obligation to write an SCP and if you do so before you're ready, it'll probably bomb, USE THE SANDBOX, yada yada…"
I know we have introductory pages, but I think it is highly unlikely that a lot of new users read even half of it, which is their loss and they deserve to get downvoted, but I think that the reactions to bad SCPs and the shitstorms that ensue on the discussion pages are not worth the effort, and are best avoided.
However, seeing as I am pretty much a newbie myself, this is merely a brainstorm based on my experience and can be liberally ignored.