Surveillance of the users' reading lists, obviously.

Thats what a very large part of the computer industry means when they talk about "monetizing" all of the "big data" they suddenly have. Go back over the last ~decade of goods and services made by internet-related businesses, and you can see a clear trend towards turning features that used to be stand-alone (browser bookmarks), into "free" services. Often this makes the product mildly worse (latency, uptime), which is then lampshaded with a minor feature like bookmark-syncing (which could be done in other ways that do not betray the contents to a 3rd party).

If you have any doubt about anything I just said, I recommend watching the talk I've been suggesting lately by Aral Balkan ( https://projectbullrun.org/surveillance/2015/video-2015.html... ). If it wasn't obvious why Pocket was being pushed instead of improving bookmarks, then Aral's talk might just terrify you.

A reading list, be it a feature or service, has a workflow suited to easily add and remove articles and view them as a simple list. You can do this with bookmarks — and I do at the moment because it's the best way I've found to sync between Fx on desktop and Android — but there's more friction when managing articles.

Indeed! I've asked this a couple of places and got no answer. If it is functionally equivalent to dragging the address to a bookmark-bar folder called Pocket I become very suspicious of motives.