The ability to watch profiles without being on the Trusted List has been on my personal wishlist for about forever. The hoops I've had to jump through just to watchlist an ancestor's Open profile have been excessive. I have sent many requests to profile managers asking for Trusted List access so I can watch the profile, and I've gone through several Unresponsive Profile Manager processes just so I can be on a watchlist. Many profile managers readily cooperate, but I've found some who don't understand the request or inform me that they won't grant Trusted List access to anyone who isn't a close family member. I don't enjoy having to beg to a profile manager for the opportunity to watchlist a profile of an ancestor that I've edited extensively and they haven't touched since creating it by a gedcom import in 2012. And because I know that a trusted list request generates email to every listed profile manager, I often hesitate to request access to profiles with more than a couple of managers. Sometimes I'll send an email or a private message to one manager asking them for access, but after discovering that some managers can't figure out how to add an email to a trusted list, I will only do that if the manager is someone who is known to be WikiTree-savvy.
Unfortunately, I've been told in the past that it's not possible to disaggregate the watchlist function from the Trusted List function.
But a bit of good news: If you are on the Trusted List for a free-space profile, you will see page changes in your Family Activity Feed.