silva document layout enhancement proposal

Greetings,

I ran this by Kit, and he suggested the conversation be broadened to include 
all of silva-dev.  I've also created a launchpad issue so this doesn't get 
forgotten, https://bugs.edge.launchpad.net/silva/+bug/177171.  Here's the 
text of the issue:

We've noticed that it is difficult to get "advanced" layouts for a silva-based 
web pages. Sure, you can use a code source and embed documents, positioning 
with CSS and such, but a non-technical person isn't capable of such things. 
Most of the content in our CMS is generated by non-technical folks. They 
stick to what they know: one page with simple top to bottom text and rarely 
any graphics.

Here's a proposal for Silva (document) to transform to have more control over 
document layout:

1) the web design team, while creating the identity/look/layout for the site, 
also specifies a few "standard" page layouts (e.g. full-page, two-column, 
floating box on the right, content on top, then two column below, etc) Each 
section of the page is a separate "page section"
2) Someone with access to the ZMI adds the code for these layouts to a service 
in the ZMI
3) When you create a Silva Document, you are prompted to choose what document 
layout to use for the page. The default is "full-page". (note that this isn't 
the same as choosing a different page layout/template when using 
SilvaLayout...SL is for the template, this proposal is for document layout of 
the content of a page)
4) When you edit the document, kupu edits the first document section.
5) There is a tool in kupu that shows which section you are editing, and 
allows you to edit a different document section. I wonder if we can store all 
the content in one Silva Document somehow, maybe with section tags.
6) There is also a facility to change your document layout to one of the other 
pre-defined ones. This isn't exactly a "preview", as it could be the case 
that new document sections need to be created, or existing ones moved around 
(e.g. news panel on right / left of main content)
7) It would be neat if there was an "advanced" layout that you could use to 
create your own custom layout.

Cheers,
Andy