Admins can set any rule they want to disallow things, but it has to be upfront and applied equally. If Admins go down the path of saying "yes" to Poster A, and "no" to Poster B on the fly or on a whim, that's a rabbit hole.
Here's why: let's say you just wing it. Project Plan A gets posted, but Project Plan B is rejected for no upfront reason (just because an Admin thinks it may be unsafe). Someone sadly gets injured after building Project Plan A that appeared safe and was posted. A legal argument could be made that because Admins had a history of exercising discretion with Project Plan B (by rejecting it), then they should have done their jobs better and evaluated Project Plan A so as to prevent injury.
Basically you are better off by staying hands off, and stating that the Forum assumes no liability (as in our Terms now). The moment you jump in and say A is allowed, but B is rejected, you've presented yourself as an authority on the safety aspect of projects, and that's a potential liability issue.
There is a logical exception—and that is a plan that a "reasonable individual" would consider dangerous or illegal. An average Joe on the street—with no knowledge of metalworking—would consider plans to make a guillotine dangerous, or a plan to manufacture a pipe bomb illegal. Admins can reject or remove these outright either based on observation or someone using the "Report" feature. You can't predict craziness, and thus it would be difficult to list ALL things like this upfront. But I can't imagine this exercise of discretion being problematic to a reasonable person or in a lawsuit. In fact a reasonable person would expect Admins to use their awesome powers for good in such cases.
I know little about climbing equipment but I suspect there are many modifications that enhance safety as well as reduce it. And not being an expert I'd not want to exercise discretion as an Admin. That sounds like the proverbial rabbit hole. In the case of lowers, I know little there as well except that in some cases it is illegal to manufacture, import, transport, possess or use (pick one or more category). Add to this ever-changing legislation (such as what's happening in Ottawa now), and you create a situation where Admins must keep current to make the right decision. I wouldn't want that responsibility.
So WRT specific areas of interest, if Admins wish to set additional rules for firearms, or "personal safety" devices that's up to them, and we shouldn't push back. These are volunteer positions and the goal should be to minimize the hassle factor to Admins. "Personal Safety" is a tougher call as this is subjective. I think this is where we will build on experience and watch feedback carefully. If a pattern emerges—like a bunch of people say Project Plan C is really unsafe, then Admins can consider removing it and adding it to a list in the Terms that are unacceptable so they never have to worry about justifying the decision in the future.
The "Report" feature should be encouraged here, just like FaceBook and Twitter do. This makes safety a shared responsibility amongst all of us, just as it should be.
Again, I think risk is low with these provisions in place. It's easy to get carried away with what-if's, but this isn't the USA. If Admins want to disallow certain types of plans upfront that's their call and we should respect it. If there is that much concern then rather than letting users post it should be submitted to Admins first—which is unfair in a volunteer group like ours, and self-defeating to the initiative at large. Otherwise, let's watch it play out, allow for Admin discretion to ban certain things upfront as they see fit, and respond as a reasonable individual would if anything dangerous or illegal shows up. If this were a commercial Forum, it would be a different discussion, just as expectations are higher for FaceBook due to their size and influence. But we're no FaceBook.