At the moment  org-element-adopt-elements always appends the new elements
after the elements original children.  In many cases one might want to
append before the original children.

I want to propose adding an argument to org-element-adopt-elements that
defines if the elements should be added before or after the children, i.e.
(if append-before
  (nconc children (org-element-contents parent))
  (nconc (org-element-contents parent) children))

Would this be okay?