Naturally I can subclass and provide a defaultPage(WOContext) but
I'm wondering how much of the D2W components/framework require a
session to work?
All of them. There is no D2W without a session. So, D2W is a good
choice for anything where the situation requires a session and
where you can live with the somewhat hard to change layout of D2W
pages - not that you can't change it, but it's not easy to get a
nice looking application.
You actually don't have to change layout of framework's D2W pages. I
usually start a project by subclassing all the D2W-pages (InpsectPage
extends ERD2WInspectPage, ListPage extends ERD2WListPage, MessagePage
extends ERD2WMessagePage, etc) and use project-specific html markup.
Java files for these pages most often have no logic at all.
So, all our projects have both admin and front-end driven by D2W. I
also agree with Anjo saying that having session is not a problem
since it's just memory and thinking about saving memory on the early
stages of project sounds like a premature optimization to me. You
normally get much more in return.