Hi! I like both ideas. Perhaps the second idea will not work together with the new superpeers concept (or 'Ultrapeer' as Limewire/GDF named it).

This File Mirrors data might be transfared together with the file data (additional http X-header) and could not only help to increase download speed but also to find rare files (something I'm very interested in).

About host exclusion, there has been a idea about 'SUPERPONG' in another thread. When more superpeers are available in future, the IP/ID of superpeers found in a horizon could be a good identification to avoid double/multi connection within the same local horizon. hehe, Limewire would call Superpong 'Ultrapong'.