Implement reinsert on demand
Provide a "reinsert on demand" feature, similar to FreemulET implementation, but as a standard feature.
This would improve sharing of large files, and would make sharing of rarely requested files more reliable.
There are doubts whether on-demand reinsert poses some anonymity risks, but individual user may be given an option whether to enable it or not, whether to always reinsert complete file or individual blocks etc.
The Keepalive plugin (unofficial so far) allows you to make sure that particular files remain fetchable. This needs further improvements and it needs to be made an official plugin, but it solves most of the above. For security’s sake, we generally want the original uploader and the people running Keepalive for the file to be different. It is planned to improve Keepalive, make it official, and integrate it into the web interface.
One option would be to allow people to choose to permanently host content.