Core Rails, however, isn't moving towards embracing the pure fat client model. (DHH has explicitly ruled out doing so.) That makes me a bit less interested in the benefit of any JS library's Rails integration.
Carlos and Santiago are active Rails 4 core team members, and Steve K. has risen among the core team ranks as well (not to leave the others out).
You can see the large overlapping of names there.
Also of note, rails-api includes ActiveModel::Serializers, too: https://github.com/rails-api/active_model_serializers/graphs... You can also find a lot of big names there, as well.