What is Remote iCloud Backup? It was listed on a slide in the iOS 11 keynote. What does it do and how does it work? My best guess is that I can initiate an iCloud backup by signing into iCloud online?

https://imgur.com/a/JLfwe#2TjEs9c
It certainly looks like that. However, there seems no way to trigger it yet (maybe it will be added to a iOS 11.x future update).

There's no trace of it on iCloud.com but something appears if look up another device in iOS > Settings > Apple ID (top) > Another Device (Bottom)

In my case it only shows - and inaccurately says Last iCloud Backup: Never so it looks like it's not fully supported yet