Subtheming Drupal 8
Themes are looking good. Especially subthemes. The small tweaks were managed by subthemeing Bartik which also includes carrying over all the settings from it.
My subtheme fixes the issues with the headings and the position of the logo. It's still a bit of a hack (the colour of the headings is hardcoded in the CSS rather than managed in the Color module (but hey... it's a quick fix)).
The first difference; Themes aren't in /sites/all/themes any more. They've been moved to the top level of the site and now live in /theme.