IANAL but I don't think that such schemes have been tested in court. Here in Germany you can get in trouble for just linking to bad content, so it seems to me that storing a chunk of it, however encrypted and inaccessible to you it might be, isn't going to be safe.
> With Freenet, it's very hard to even prove even that you host pieces of any particular thing.
It's only hard if you don't know the content. Freenet uses Content Hash Keying, where the file is hashed and the hash is used as the encryption key (so only people who either know the hash or have the file can request it).
If you have a list of cleartext files or hashes, it's not very hard to check if those are hosted on your node.
