Unregistered: We have standarts, here it's Gnutella protocol v0.4 (+ v0.6 which is just a new handshaking)... also old clients do still following this protocol, great for everyone. If we need a new protocoll, we could introduce it! If you think we need a new protocol which is not backwards compatible, just do it and post detailed suggestions for discussion. While Gnutella clients are in steady improvement, switching over to a new protocoll would be possible.... until now I haven't heard any voice we should leave backwards compatibility. Most ideas like superpeers, hashs, metadata, specialized horizons, swarming and freeloader reducing could be perfecty integrated into Gnutella, it was wisely designed flexible enough. With the new v0.6 handshaking we could do even more crazy things.
Personally I play with the idea of introducing some new descriptors (see older postings about XPING/XPONG etc or packing Query/Queryhits together), not backwards compatible... but it's just design theory yet and far far future.

John: We can compare features anyway. Gnutella allready learned from Fasttrack, superpeer ability will come soon, hashs and metadata will follow. A overview on features, advantages and disadvantages will help coders in design and implementation.