One of the custom off-topic close reasons here is
Questions on applications that no longer exist are off-topic for Web Applications as no one will ever be able to make use of the answers again. Rest in peace, dear departed app - you will be missed.
Can we expand that to also include features that are no longer available? For example, some of the Gmail Labs that have gone away? Gmail still obviously exists, but if the feature's gone no one can use it. It's not like a desktop app where someone might be running an older version.
I suggest something like:
Questions on applications or application features that are no longer available are off-topic for Web Applications as no one will ever be able to make use of the answers again.