Is https://aboutfeeds.com/ an answer to #2 and/or #5?
2 was different. I was thinking about what happens when a user clicks on a feed - it's not very user friendly, especially now that browsers just show the XML file content. If we had a mechanism that wraps that request and gives the user a way to subscribe directly via one of the many available feed reader, that would help a lot.
The idea is not completely novel, https://github.com/superfeedr/subtome goes into the direction but I think it is broken. A website carried by an independent group could be a solution. Maybe even something that could help in case browsers are open for some changes here, but don't want to create the UI part. Or when working on extending a CMS and instead of implementing that UI again, we use that mechanism to wrap the feed. As a web developer making it a website was probably an idea near to me, but there might be better solutions.
I agree. But I'm also willing to think that a simple button to copy the feed URL would suffice. Since feed URLs can be read by all kinds of reader software (and you don't know upfront which ones, definitely way too many possibilities) there's no way as a subscriber to go from a website with a feed link to your reader app without just copying that link somehow. It's too much baked in to the protocol to do it otherwise, I guess.
But sure, the button to copy the feed on by default would already be a great improvement.
https://www.rssboard.org/rss-autodiscovery
Back in the day, I think Firefox even put an icon in the address bar when a feed was available.