Current behaviour of the wiki Page Hierarchy seems to be to order sibling articles in alphabetical order. Under the Hierarchy browse-menu in the wiki-page-nav left panel, the current page's parent, children and siblings are shown. In the full Page Hierarchy reached from the Page Hierarchy link under the Page Collections browse-menu (also in the left panel), the full hierarchy can be seen from an expandable tree. In both those displays articles that share the same parent are ordered alphabetically.
In the Edit Mode of the page hierarchy users can move pages between levels but within those levels ordering is always alphabetical.
1- provide the ability to specify the order of articles that share the same level in the hierarchy
2- change the default order of pages within the same level to the order they appear on the page, rather than alphabetical
Either one or both of these would be beneficial to me. I see #1 as the more flexible of the two, but personally I suspect if I had #2 I wouldn't use #1 that much