Thanks! There are still new ARGs out there, though IMO not as focused on narrative or worldbuilding (especially through websites) as those in the 2000s. You're right about the fractured community, and I think to some extent ARGs are getting less accessible because they're hyper-targeted to specific communities that might be harder to discover or join.

Six to Start is doing well and we still play around with ARG-like ideas in Zombies, Run! for our seasonal virtual races :)