It isn't about niche celebrities, but celebrities as a whole is their niche. And journalists, of course. Newspaper websites publish vast quantities of tweets because it costs them nothing, it means you indirectly consume a lot of tweets.
But the celebrity content consumed by journalists is as a whole still a niche, even if all celebrities are on there.
FWIW I think it would be a mistake to abandon that, but it does raise questions about how they grow.
Chris Sacca said a lot about this recently. http://lowercasecapital.com/2015/06/03/what-twitter-can-be-2...
Except Instagram has more active users than Twitter...
It's not about active users, it's about how it's used.
> Everyone had an AOL keyword. AOL isn't dead, but it fell hard. Ubiquity isn't enough.
Every business having a Twitter account won't save Twitter any better than everyone having an AOL keyword saved AOL.
Had AOL built itself as a web portal like Yahoo from the start it may very well have stayed relevant. I still have business partners (in non tech fields) that use their AOL email and news/portal services.