It would have the ability to be extremely versatile. It can be seen as a traditional bookmarks bar but also with an interface. Of course, there would be features like how you'd sort them, cross platform compatibility, support for popular third party applications (Pocket, Instapaper, etc.), and much more (which have pretty much been stated already).
The most important feature to me, would be to figure out a way to sort my bookmarks for me based on my current population of bookmarks, my browsing history, and of course, what the actual bookmarks are.
The most important feature to me, would be to figure out a way to sort my bookmarks for me based on my current population of bookmarks, my browsing history, and of course, what the actual bookmarks are.