This feature already exists in a way: not sure if it's a Linkify-only feature, but the circle that represents your post count gem has a green border when the player in question 1) is online and 2) has their privacy on in-game. Linkify adds the description of "online: <status>" when hovering over it, but not sure if the green border appears even without Linkify.
This is specific to Linkify.
~~~~ Just another victim of the ambient morality ~~~~
~~ Founder of the Caped Carousers quest cape clan ~~