I have no issues with org-struct-mode being removed.  I used to use it,
especially for emails.  I now simply change the mode to org, write
whatever content I want, and then switch back to message mode to send my
email.  Works fine and gives me the full power of org.

-- 
: Eric S Fraga via Emacs 26.0.50, Org release_9.0.9-787-g197c58