I think it would be really handy if your bookmark bar could be specific for each workspace.
For example if I use my gaming workspace on a second screen while playing for game guides and wikis, I'd like to have my bookmarks for those guides easily accessible in the bookmarks bar.
When I later want to do some online shopping and switch to my shopping workspace, it would be cool if it automatically changed the bookmarks bar to my shopping site bookmarks.
I think customizable bookmark bars that automatically change according to the selected workspace would really enhance the usefulness of the workspace feature overall, instead of it only being kind of a tabs folder feature at the moment.