There are situations where a resource is blocked, but transparently. For example, the pirate bay is blocked in some countries. However, it's done publicly, and that the site exists isn't denied. The ISPs that effect the blocking could use this status code to inform people who try to visit it that the site does exist, but they can't access it because the government says so. This could, in theory, divert activity towards the ISP (which has nothing to gain from implementing such blocks) to the government. That is, instead of spamming the ISP's helpdesk, they could petition their representatives.
Of course, in some situations the block is supposed to be also denying the existence of the site, and in such cases this status code wouldn't apply. That's mentioned in the RFC (section 4.1).
Maybe, but if I have to guess differently than you think: They probably want to use this to "troll" governments and heavy users of DMCA take-down notices. These people usually don't like it if users notice that they were responsible, so this is against their interests.
