CAPITALS, Title Case, or Sentence case should have zero impact on flagging something as spam in regards to email filters; you can try this yourself by modifying the language string to show whatever casing you'd like, that's why there is a language editor.
CP -> Display -> Languages -> mailer.php -> "DAUA_SUBJECT" string.
This will not be changed in the future, it's never been an issue before and admins are welcome to customize their language strings.
