Le sigh...
"Let's all think of the clever, and not think of the function...."
Yes, it might put up a bit of cost, but how hard is it to also incorporate a remote sounder, like most wireless doorbells? Or even some local (encrypted) storage, so it can take/store pics of people who did come to the door?
If your internet backhaul is down, isn't the result going to be the same? At least Hue & Lightwave etc continue working with whatever settings they have been given, if the cloud goes down. My home automation system uses a cloud UI to configure, but once it's got it's config. it doesn't need the internet.
Failover modes people, failover modes....