DNSSEC deployment is growing steadily:

  https://stats.dnssec-tools.org/images/totalds.svg
  https://stats.dnssec-tools.org/tld-graphs/com.png
  https://stats.dnssec-tools.org/tld-graphs/net.png
  https://stats.dnssec-tools.org/tld-graphs/org.png
  https://stats.dnssec-tools.org/tld-graphs/biz.png
  https://stats.dnssec-tools.org/tld-graphs/info.png
  https://stats.dnssec-tools.org/tld-graphs/us.png

The USA is #2 behind Germany by number of DANE-enabled MX host IPs:

  https://mail.sys4.de/pipermail/dane-users/2020-April/000553.html

The USA is not always the best practice to emulate. Microsoft's SMTP servers host mail for at least 284k (today's count) signed domains. When they enable inbound DANE, these (likely more by then) will be protected by DNSSEC and DANE.

The rear-view mirror is not always the best guide to the road ahead.