Some feedback from someone who's running a customer support SaaS with some thousands of users. Tickets is our core feature. And we indeed have the requirement

Some feedback from someone who's running a customer support SaaS with some thousands of users. Tickets is our core feature. And we indeed have the requirement to show that 'Someone is also viewing this ticket'. But the more important feature we need is to sync changes to a ticket across users. For example, if user X re-assignes the ticket to user Y, people who are viewing this ticket should be able to see the change without refreshing. Knowing someone else is also viewing a ticket is not particularly useful for a ticketing system, because even if I know a ticket is viewing by others, I still need to do what I'm supposed to do (reply, re-assign or whatever). I guess Also Viewing is great for websites where users feel comfortable doing something with others, and they don't make much changes to the UI. For instance, watching videos or listening to music with friends. By the way, I personally know Paul (the author) and I wish Also Viewing could become popular.