Similar to a Web Viewer control, except that a layout viewer would embed another layout within the current layout. Parameters for this tool (off the top of my head) would be layout and TO... obviously would have to be related to the current layout's base table.
Would allow creation of common elements like navigation bars, lists, etc. that could be created and edited in one place and reused ad infinitum elsewhere.
EDIT: Another parameter would be "View", e.g. form, list, or table