1. Bookmarks as Default Home Page
This feature is not yet there, I asked developers about it, so hopefully in the future updates there will be this option available.
2. ‘Mark All Topics As Read’ feature
Yes, there are ‘Dismiss’ options for New and Unread, but they will not gray-out until you ‘read’ them (just visiting the last post in the topic will gray them out).
Under your Preferences > Notifications page you can play around what is “new” for you and on Preferences > Notifications > Categories page you can fine-tune which categories will be muted for you.
I followed some discussions about “ALL READ” feature on Discourse dev forum and founders are opposing to implement this feature (for now) cause it can cause confusion and break some tracking functions.
We will add this to our features whish list and see how we can add it in the future.