It's not a fad at all, with Netflix and other companies using Rx in all flavors on their platforms. See this video from Jafar Husain, a tech lead at Netflix, talk about how they use RxJS at Netflix:
https://www.youtube.com/watch?v=XRYN2xt11Ek
Ok, the consider GitHub for Mac and Windows are both written using Rx frameworks. In addition, so is Cortana from Microsoft and has been in the phone ROM since day 1
FWIW I don't think FRP is a fad, but big companies have lots of projects going on all over the place and it isn't uncommon for an engineering team to be given permission to trail some tech, especially at an OSS shop. Netflix might have some team(s) using some Brand New Library but that isn't sufficient evidence for that tech not being a fad. Switching costs are high at companies that remain in business and are growing so it's not uncommon for a big shop to have some random tech written in fad code that people absolutely despise in the future.
