no such “virtual” folders are currently not supported. Based on customer feedback we are currently investigating mechanisms to open shared calendars through separate accounts (without the need to know the users credentials of course) as part of https://jira.kopano.io/browse/KOE-124.
Reloading with F5 reloads your selected folder and you can only select one folder at the time.
What you perhaps can do is create a plugin yourself and enhance the F5 keybinding handler to
reload the hierarchy - e.g. "container.getHierarchyStore().reload();"
Not exactly what you’re looking for but if your shared folder contains a new item the counter will be updated this way.