This (having a column always showing device content) seems to me like something that would have been asked for before, but I don't know where or when.
Looking at the Reading List & Calibre code, Calibre has signals fired when a device is connected or disconnected, but disconnected is triggered
after the disconnect; ie, too late to update a Reading List.
Attached is an experimental version of SmartEject that will ask if it should Sync if there's a list that could be sync'ed. Unfortunately, it can't exclude lists for other devices or lists from searches.
If this works for you, I will consider making it a silent option.