Well, here is some feedback. In short, I Oppose the Flow idea.
From the description, it sound too much like it will be exactly like a Google+ stream, mixing everything together.
- Neither indentation with colons nor signature requirements are opaque. They are different from other sites, but it is not at all difficult to grasp and get a handle on. There is plenty of documentation on how to do it, and it is easy to pick up from how other editors do it.
- I agree it is not 100% clear where to hold conversations. Most editors specify in their talk page where they want the conversation to take place. This shouldn't be an issue. Talkback templates do the job just fine.
- Knowing what a watchlist is is not as big a deal as it is made sound. Any editor wishing to seriously edit will find the outline of the star on the top of the page and realize it is for their watchlist.
Why the pictures? Are we a social network now? Will we be forced to add a profile picture?
This sounds a lot like it will take away some of our abilities to manage/moderate/deal with our talk pages. Definitely not good.
I would suggest the focus of flow be more along the lines of additional features, such as private messages, instead of increased user-friendliness. If flow is just for user talk pages, new editors will still have to learn how to use the current system for article talk.
I'm not advocating "if it ain't broke, don't fix it." Focus the features development on helping active, experienced users, not limiting them. The biggest problem with editor retention is not the difficulty of the interface, it is policy and the bureaucracy of WP that make it so unwelcoming. The steepest learning curve are all the rules, not the UI. Don't make it harder for experienced editors.