Many here will hate this because they are so in love with the internal combustion engine, but what will revitalize GA as well as motorcycles is when they go electric. The folks here that have electric cars now understand why. Electric propulsion is just so much better and it is actually new. Historically new and better airplanes have often come when new power plants come online and I predict this will be the case again in the future. If you want to engage millennials, offer them something that is actually new, not Cessna 172s and Harley Davidsons that are their grandpa's and even great grandpa's toys.
I know the time is not now and we must wait some more, because batteries are just not good enough for airplanes and not cheap enough for motorcycles, but it is coming. It will happen though and when it does, there will be a renaissance in all vehicles. I personally can't wait!
As an aside to the off topic part of this thread, I have been flying for 20 years and I own my own plane, but I've been playing video games even longer. I'm in my middle 50s and I regularly play COD multiplayer online. I am one of those that does watch other people play COD on YouTube.
The key is, you must have a personal connection to the game. You have to have played it competitively and understand it's nuances and complexities, then you can enjoy watching someone else play the game that is better than you, or enjoy watching a great match between professionals. That's right, there are professional video game players.
I can't understand why people would want to sit around watching people play soccer, or golf, or hockey, or tennis, or even basketball. Those are some televised games that bore me to death.