The first two cases you mention are about communicating with a specific real world organization. You can implement it using ipns, but it's inherently centralize

The first two cases you mention are about communicating with a specific real world organization. You can implement it using ipns, but it's inherently centralized. The last one is a no. Well actually yes if you just poll a file, but that's not practical on a large scale. You need an external communication channel to implement that. It's possible to have that be fully distributed as well though, as in tox. You need this external communication channel to implement a lot of things anyway, so it would probably be part of the platform that forms around the idea of a distributed web.