Ideas

… or the service that would make dn42 truly interesting for people (for non-technical reasons).

it should be difficult to setup on the Internet (for technical or legal reasons)
it should interest people that are likely to know dn42 (hackerspaces, etc)

Any idea, apart from pr0n? Multicasting video flux?

Ideas for stuff that are technically difficult on the Internet:

multicast routing (well, it doesn't work in dn42 either)
something that depends on the network infrastructure or topology (e.g. a game where you have to announce things with BGP)
CloudStack Implementation to test fail-over to different locations
Open Plex Media Server - Anyone within dn42 would have unauthenticated access to the media.
We need to branch out to events etc… have talks, streams and increase our media presence.