Thanks!

1. There isn't a good way to do it: your All tab will be full of potentially illegal content if you federate with NSFW instances. We want to focus on dev, and not on legal issues, so for that reason we won't federate with NSFW ones.
2. I'm guilty of this also w/ jerboa, showing lemmy.ml content before you log in. We obvi don't want single points of failure, and want lemmy to be as distributed / spread out as possible. If some of the bigger instances go down, I'm sure people will write premature articles about "the death of lemmy". We're still in the early stages, and I think we'll have to see how things evolve, and what promotes decentralization the best. We've tried to rotate the signup sites at the top of join-lemmy.org , but there are likely other things we could do.
3. Creating multiple types of NSFW would be possible, its just not something we've implemented yet, and there are also issues with how that would be handled with activitypub, which only has one type of sensitive field.