wouldn't it be enough to work on with gnutellaclients, but distribute a host-list according to this special interest.
Normally you are not in a network with all the gnutella-users, but with a small subset of them in a "horizon". This horizon develops with your searches (your interests) Thats like it is.

So it would be a small step to build horizons by distributing host-lists ordered by special interests. (Not gnutellahosts.com but gnutellahosts.80s.com)

It may not be the best solution, but it should be effective