@mwlucas I feel that TLS/ACME/LE has a broader application ("know this one fundamental thing") and lower barrier to entry, that it fits better with the "IT Mastery" series theme.

That's not to say DNSSEC isn't also important, but I feel it's a more advanced topic with a lesser reward compared to getting people to use TLS and understand why they should use it.
Also, the number of DNSSEC-validating resolvers feels (subjectively) low, but all modern browsers check TLS and complain loudly.