Our regions aren't identified by predictable id attributes. In the core themes we have leftover ids like "sidebar-left". Other regions - e.g., 'header' - have no id attributes.
This presents theming issues and also barriers to dynamic content rendering; there is no way to dynamically assign content to a given region.
We should ensure that all regions have an enclosing element with an id like 'region-left', 'region-content', etc.