Currently, the regions specification is agnostic to what can be a region. It assumes there is a selector for an element or pseudo-element which provide a way to make the generated box a region.
In has been suggested (as in the URL thread), that regions need to come with a solution for creating blocks that can become regions in CSS.
One view is that the issue of generating new blocks through CSS is generic and not limited to regions. Another view is that currently, the only way to create regions is with elements and that it limiting and promoting a practice some see as improper.
Paris F2F - the WG discussed the issue and agreed to close it once the CSS Page Template module is proposed.
The working group resolved to close this issue. We have demonstrated that named flows work with every CSS box-generation mechanism that has been defined or proposed.