I may sound paranoid, but on my communities, I have more and more requests to remove past content. In a few months, EEC is gonna pas "right to be forgotten" (not sure of the english words) laws that will basically force us, forum owners, to comply with requests asking to remove each and every little message someone posted in the past X years.
This is were it's getting tricky ; INCLUDING QUOTES. Of course the law does not speak about quotes, but it is, per se, user content protected by these laws. A quote is in fact an unauthorized copy (and this, since day one).
I believe that "forums from the future" should limit the way people quote each other, and especially the "quote "button should create "soft quotes" (links to the quoted content, maybe ajax loaded) that would get blanked out when an user asks to leave the forum and have his content removed.
I understand this is a long shot to some people, but I'm sure requests like this will be common in a few years. May be time to start "re thinking quotes" soon.