I was about to ask the same thing. I'm on 2.9.0.0 and unfortunately moving systems to archived status still taints dashboard/software statistics.
Is it possible via configuration or (simple) hack to disregard data from archived systems when browsing in the dashboard, all software etc? If not, then "archived" as is is not very useful unfortunately. We'll have to delete all archived systems in order for the dashboard to display meaningful asset information.
If this function is not implemented in 2.9, then please consider it for a future inclusion.