Wysiwig editor for .html files not .htm content files

Is it a mistake or planned feature?
Default extension for content files is ‘htm’ And now editing is in ‘code editor’.

Yes, see the Release Note for v3.2 here: Release Note 33: October CMS 3.2 - Page Finder Release - October CMS

Editor Content Types

When editing CMS content files via the Editor in the admin panel:

  • if the extension ends with .htm it will show a code editor (previously rich editor)
  • if it ends with .html it will show a rich editor