After scanning some of the more promising subreddits, I made a few notes:

/r/augmentedreality

  - 6K Subscribers
  - Demos of things people have built
  - Promising

/r/virtualreality

  - 39K Subscribers
  - Mix of gaming news and "see what I built" articles

/r/vr_ar_ux_design

  - 220 Subscribers
  - Very UX article heavy

/r/AR_Innovations

  - 1K Subscribers
  - Mix of consumer news and development resources about AR

/r/virtuality

  - 1K Subscribers
  - Mostly hype about VR, few development resources

/r/Vive

  - 77K Subscribers
  - Mostly about gaming, not development