This is also a critical feature for me. I would add that for implementation, it could (for my workflow) be as simple as adding "Select Bookmarks Bar Folder" as an option for Command Chains, as it would be simple enough to sort all workspaces into separate folders. If that is a separate feature, I can make a different request, but it's surely related.
I can see how that may not be an optimal implementation for other peoples' workflows who don't use custom buttons / command chains to switch workspaces.