Edit: I was originally talking about both safe mode and donmai.moe in this post before I understood they are two separate things. I fixed it to avoid any more misunderstandings. Everything below is for donmai.moe only, not safe mode.
After trying out donmai.moe, I noticed some major flaws with how it currently operates. The main issue I noticed is that any new upload rated G will instantly appear on the front page regardless of its contents. That means that if a user were to upload hentai and rate it G, there's a decent chance donmai.moe users will see it before the rating is fixed. We need a more proactive approach to these situations. While our options are limited due to the site being entirely volunteer-driven, there are a few things I think we could try.
All of these ideas are meant for donmai.moe only and should not affect the viewing experience of the main site.
Completely hide status:pending and status:deleted posts
Note: By "completely hide," I mean treat them the same way non G-rated posts are: completely inaccessible without changing the settings.
As we all know, new posts uploaded by members below Contributer level get put in the moderation queue and have 3 days to be set active by an Approver. They are still visible under normal settings during that time. Hiding pending posts will give other members on the main site time to fix the rating before it is visible in donmai.moe mode. Approvers could also check the rating before approving or deleting posts (this should be a very quick check; I don't expect them to try and resolve G/S disputes). Even if some Q/E-worthy posts make it through, they'll at least be off the front page. And while we can't always rely on Contributers and above to rate posts properly, we probably don't have to worry about them putting anything extreme in G.
Users of donmai.moe can still search for deleted posts, which I think are less likely to be rerated due to them being hidden by default. It may be worth considering completely hiding these posts as well.
Completely hide posts uploaded less than 3 days ago
While I did say Contributers and above probably won't pollute the G rating too badly, there's still the possibility of one deciding to go rouge and deliberately upload hentai as G to spite Danbooru. If we want protection against those kinds of events, we may want to consider applying the 3-day buffer to all users. This will of course mean that donmai.moe users will always be 3 days behind users of the main site, so this isn't a decision to take lightly. If 3 days is too much, then we can set a shorter time.
Completely hide posts with / wiki entries of NSFW tags
Some tags such as sex should never appear on G-rated posts. Hiding posts with these tags can provide extra protection against misrated posts. However, even if there are no results in the search, the user will still be redirected to the wiki entry. I think the wiki entry should be hidden as well because it is hard to discuss these topics in a SFW manner. To summarize, I think there should be absolutely no evidence of these tags being referenced in donmai.moe.
Add a policy to encourage SFW writing in wiki entries
If hiding a tag is unreasonable because it could still potentially be used in a G-worthy post, we should at least try to make sure the wiki avoids NSFW topics or language unless absolutely necessary. Adding a policy may be unnecessary as it would be hard to enforce and most wikis describe things in SFW terms anyway, but I thought it would at least be good to bring the idea up.
Updated