I guess what you’re calling “System events” here is what I called “Page Notifications”
Indeed, sorry for that.
Probably, but it’s not currently the case by default in the wiki.
Currently, the first user of a wiki (e.g. admin when running the demo distribution) watches all the pages (because they watch nothing) but doesn’t receive any notifications because the Page Notifications are disabled in the “Applications” section (btw, didn’t we say we’d call that “event types”?).
So it’s discoverable but not really, the administrator still needs enable notifications on the wiki, and they would do that by going to the global notification administration and configure the event types to enable page notifications. So it still requires an action from this first user running the demo distribution in order to make the feature discoverable.
This is what I meant in my previous message when I said that we seem to be focusing management on event types when we should focus them on locations.
And this is also what I meant that we’re doing opt-in by starting with an opt-out and then hacking it.
Now, this way of doing things was probably also limited by the absence of the global filters, today (after XWIKI-18406) it would be simpler to allow the admin to enable notifications everywhere (to make users discover them) even if the default would be that they watch nothing: the admin would just need add a global inclusive filter for the whole wiki and notifications would be pushed to all users. Thus, we don’t really have a reason, from my pov, to keep the behaviour of “not watching anything means watching everything”.
One more argument against this behaviour is the fact that once the administrator activates the event types in the global administration, all users receive notifications for all locations on the wiki (including, for example, the XWiki space). The fact that users receive notifications for the XWiki can be a problem, and in the past the absence of global filters made it impossible for an administrator to fix it otherwise than by deactivating all notifications or running a script to update the notification preferences of all users.