In the strict P2P concept, your friends or contacts may well get annoyed if you keep hitting their phone with requests for the same image for example.
Caching and decentralized content are 2 different things I guess Well this is a mailing list of people who, more or less, are using technology and/or cryptographic science to ensure privacy for "anyone"... In such a task, caching appears futile, unnecessary and an obvious risk. Therefore, better not to even considering it, that solves the issues. I develop an embedded system for a secure communication station. I want everything to stays transient, to be erased as soon and as fast as possible. I don't want that it is possible to scan the memory to intercept any variable, deciphered stuff etc... In that communication station, communications can be eventually extremely scarce, internet very slow in extreme environments with all sort of modems involved. Since this is a secure communication station, the last thing I want is to cache anything, simply because that is a secure system. The received data are stored in encrypted external components. Etc...