After some lively discussion yesterday (more references below), here are my thoughts.
We need to come up with something that's easy for the publisher. If it's not, this has approximately 0.142% chance of widespread adoptance.
MIME types alone do not solve the problem - lots of discussion about this on yesterday's post.
Escaping the URL after feed: is going to be way too error prone. Look how many feeds don't correctly escape their content - this is going to be much worse. Which means tools will have to deal with correct and incorrect forms both...so let's just do it the easy way.
Having a "standard" port for aggregators to listen on is a bad idea; and in fact, many folks (including me) would argue that having the aggregator listen on any port is a bad idea.
We're not developing a new protocol - this is merely a hook into the browser and the shell to make it easy to subscribe. The characters "feed:" will never go across the wire in a request.
Keep the comments coming! Let's try to hammer this out soon - we're all in this to increase adoption of RSS...and arguing over MIME types, parameters, and escaping doesn't get us too much closer to that end.