Being able to archive workspaces so it's removed in the sidebar without removing access to the members would be really helpful!
I agree being able to archive or hiding workspaces with completed projects from your default view would be fantastic. Or adding a filter to the workspace view so you could create and save filters as needed to show only workspaces desired. As others mentioned in the comments, this need is growing as workspaces are created per project or group of projects since you cannot grant access to folders in a workspace only sheets or at the workspace level and there are different people that need access based on project. Also the way we use smartsheet, it does not make sense for all to have a license so we cannot use the workapp option to separate access.