Basically what the title says. Just add a feature that lets you follow other users to get a notification whenever they post.

Either set up a feed to check every hour or so, or just bookmark their post search (ie user:furrin_gok) and check that when you pop on. I'm not sure many users would make use of a user based subscription over a normal tag subscription.

I imagine this request will meet the same fate as the requests for tag subscriptions, which usually get shot down saying that it's incredibly resource intensive on the server for people who may or may not even come back to check for the updates.

If you're using e621 on a PC you can install the RE621 userscript which adds this functionality + many more useful things.

Hydrus could probably do this if you put in the effort. Although unless you are watching like 50 different things it's not worth it.

I can HIGHLY recommend re621 tho. It's great for small watches like this