when theme developers say their theme is “bbPress ready”
it usually means they followed this guide https://codex.bbpress.org/theme-compatibility/
Are there special features included in bbPress ready themes, if so what are the features called?
There could showing post count below the author avatar but you can easily do that by installing Robins plugin https://wordpress.org/plugins/bbp-topic-count/.
I have seen some themes have applied styling to some unread posts plugin , but really nothing too crazy that you cant get with free plugins and doing it manually without causing a hard time developing.