Sorry to be late to the discussion. @mipmip I also started with RubyCocoa long, long ago and have retained a license from the very beginning of RubyMotion. For me the most exciting announcement (OK beside Amir taking over) was OSX support. My primary interest has always been in apps for the desktop.
As to the activity in the community, I would add my voice to encouraging you to join the Slack channel. As a Rubyist, I would also suggest you join the Ruby on Rails slack channel as well (a 2 for 1 deal, can't beat that!). Heck also come join the CoreIntuition slack channel to hear from regular iOS and macOS indies to boot. And when it comes to Twitter, I follow lrz on twitter, there was always lots of stuff about beer and sushi, can't remember much about RubyMotion.
I understand your concern about "Can Amir does it all alone?" But my answer is slightly different than Amir's. I don't think he should have to do it alone. We are a community and as a community we will thrive or wither. I believe that pitching in, shovelling the snow from sidewalk of the elderly lady 2 doors down, cutting your neighbour's grass when they are away on vacation makes your whole community better. Earlier today I had an issue after updating to High Sierra. Within 15 minutes of posting on Slack, I had two different people point me to the answer. That kind of response (exclusive of all of Amir's hard work) makes me believe the community has life. This means that you don't need to depend on Amir alone to answer all the questions from newbies and long-timers. I can think of at least 10 names off the top of my head that are willing to help if they can. Amir answers more than 80% of the questions anyway but that is just because he is Amir. My point is, if we all pitch, the effort to help newbies get going is light for everybody and we can let Amir focus on the hard questions that need his expertise.
Amir focused on what was necessary to maintain the core of RubyMotion but there is so much more that you could help with. Amir has set up the rubymotion-applied GitHub repo where we can all get the documentation into a usable current state. This alone is likely the biggest hurdle for new users and one of the big marketing impacts, being able to point to a set of easy to use and implement samples to get going. The technical expertise needed for this effort is low and the payback to the entire community is huge.
Personally, I need to commit myself to participating more in a productive fashion. I think I should be able to create 1 page a month for the tutorial site. If we had 3 other people willing to do this alone, the tutorial site would be great in 6 to 9 months.