Well, what I'm thinking of is the interface widgets at page-top: the alert/notice icons. Presently they're a random mix of content and communications-related stuff (in both of the icons). I would rather have one, maybe with an icon of heads talking to each other, that is all about talk-page activity (probably including pages not in talk namespace that have been configured to behave as talk pages, such as administrative noticeboards); and another one that is all about content (maybe with a pencil icon or something). The current "bell" and "letter tray" (I think) icons aren't really meaningful.
What we have now, at en.WP, is an Alerts icon, which has a bit of a confused purpose, showing pings (communications/messaging stuff), posts to one's own user talk page (comms), failed pings by you (meta-comms), reverts (content), "you've got e-mail" notices (comms), and I'm not sure what else.
Then we also have a Notices icon, which shows Thanks (comms), "The page X was connected to the WikiData item Y" (meta-content), notices that a page has been Reviewed (meta-content), and I'm not sure what else.
Very confusingly, both of these icons have "All notifications" and "Preferences" controls, that go to the same pages! And there is no way to determine which of the two categories any of these things should be in, and there are very few of them, mostly of weird stuff the average editor doesn't feel a strong urge to be notified about.
I think this is hopelessly muddled. My guess is that the idea was to use "Alerts" for "stuff we think you'll consider important" and "Notices" for "stuff we don't think you'll care much about", but this is wrongheaded, since different users care about different things, and there is no reason to have an interface widget devoted to non-important stuff anyway.
It would make much more sense to divide these between communications/messaging in one icon, and content plus meta-control of content, in another, with separate "all notifications" trackers and separate preferences. E.g., I might want to exclude Reviewed notices entirely, and mark WikiData notices as high-priority, and so on.
Then add ability to track more things to each, e.g. to "subscribe" to notices of new posts (something with a new sig and timestamp) to a talk page or even a specific thread at one, on the communication side. Or be notified of any changes at all to the content of a certain non-talk page. And whatever. I'm sure different people could come up with a dozen different things. One could start by seeing what the watchlists already have as options, and working them into the notification system as things that can be selected for notifications.
This would not make the watchlist obsolete. I have thousands of watchlisted pages, and if I'm in "Today is Watchlist Day" mode, I may spend all day poring over non-minor edits at all the billiards articles I'm tracking, or whatever. It's a convenient tool for many things, especially when one learns its filtering capabilities. But it is not a notifications system; it's a destination ones goes to. The extant notification system is mostly showing you reverts and pings and user-talk posts in one tab (i.e., that which is likely to trigger an adrenalin spurt!) and trivia we do not actually usually need any kind of interruptive notification of at all in the other icon. It would be better for both if important (not just potentially alarming) stuff could be made to produce continual streams in both icons, one focused on inter-editor communication and one focused on non-talk content (articles and policypages, basically). I would like these to be active all day long, not with rare blips in them.
This is not the only site with problems in this area. E.g. NexusMods.com has a single notifications icon, and it commingles mod upgrade notices (content) with notices that people have replied to your forum posts (comms), which is very unhelpful and frustrating.