Hi Crispin,
I found that the manifest file does work if I add a link to it in the head section. It doesn't seem to automatically find it in the root, but it might be because I'm using extensionless urls in my testing so the blog url is /blog
Possibly Live Writer is interpreting that as a folder named /blog and looking for it in that folder which does not exist, but using the meta element I can point it to the manifest in the root and it does respect the indicators for new category support.
I am going to look into the idea of supporting editing "pages" but their model of pages is different than ours so I don't think a perfect solution is possible but perhaps an imperfect one that is still very useful. The problem is that the concept of page in mojoPortal is just as a container for features and multiple instances of html or other features may be on the page whereas in the wordpress model pages are one to one with their content so editing a page is editing the content.
What we might be able to do is implement something to simulate that one to one correspondence between content and pages. For example we could define that the first html content element in the center pane that the user has edit permission on is the page content and we could possibly encapsulate it in a way to make that content instance editable from WLW. Support for adding new pages would entail creating a page with a single html instance in the center and creating the friendly url. I'm not entirely sure this idea is feasible, but I like the idea of being able to edit pages in WLW and plan to give it a try as soon as I can.
I've been working on our live writer support for the past couple of days and have replaced our previous implementation with a cleaner one with easier to understand code based on the implementation from BlogEngine.NET. I will probably push these changes to the default branch of our source code repository later today.
Best,
Joe