Yes.

Not required, but you can do it that way (I have it with my mediahackers site). But each one is a river, not the whole thing.

True. By arrival date. pubDate is not important for ordering.

You could leave out the excerpt and it would still be a river. The important thing is that the excerpt be of determinate length, and short enough so you can see a lot of items on screen at the same time.

Does not show edited items again.

Correct. No notion of read/unread.

Not true -- you can do whatever you want there. I include a RT link on my items. Just as long as it's small and doesn't interfere with skimming.

Not required. It would however be useful to have a standard here. I want to write all my displayers in JS running in the browser.

Of course it could be an IOS app.

The main idea aren't the details, but the way its used. I can scroll back to the point where I hit something I seen. Quickly. My memory is perfectly capable of telling me I've seen something before. You can rely on it, people can do this.