An update from yesterday.
My A3 boarding pass welcomed me to the Star Alliance Lounge, but...the other concourses are now blocked off from public access immediately after security. This means the Star Alliance Lounge is off limits until traffic picks up and non-E gates are actually needed.
On the bright side, the Plaza Premium Lounge opened September 10th and is a nice place to relax pre-departure (the BA Lounge next door and nearby Casa Alitalia remain closed) which is frustrating for frequent travellers like myself.