I've struggled to find a real reason to get into learning UWP. Without Windows phones it just isn't compelling to move from WPF. Especially, when you are talking about applications that require high information density.
I assume you're referring to the constructor for the command. The Execute() method for an ICommand doesn't return a value. It's considered to be, like event handlers, an acceptable place to use async void.
Since we're talking about pronunciations... It's "ternary" (turn-a-ree) not "tenary" (ten-a-ree). I believe Robert mentioned it being added to the language at version 6. However, it's been with C# since the beginning.
@SteveRichter: Because business uses it and desktop applications remain the best choice for targeting many aspects of the enterprise. I prefer desktop applications in other situations as well, but that can be debatable.
The length of the show should be whatever the length needs to be. Don't make it a certain length for an arbitrary reason. Make it 10, 20 or 30 minutes long, whatever the content dictates. Don't add filler or cut content to make it a certain length.
P.S. reCAPTCHA is fine; sure it's an annoyance, but it's unfortunately necessary.
One other point I wanted to make on the video is regarding sealed classes. In the video you indicate that a sealed class is a code smell. I strongly disagree with that sentiment as do others. For example, Jeffrey Richter wrote about it in his book CLR via C# when he said it should be the default for new classes.
There are run-time optimizations that are available for sealed classes according to the language specification 10.1.1.2; and more specifically with versioning a sealed class can be changed to unsealed later and not break compatibility and methods in a sealed concrete class can be called non-virtually.