I've heard this a lot since around 2012/13 when I first became aware of C9, and even gave it a go. Granted it was and is impressive as a technical achievement, but I really don't see the use case at all, other than as something to use as a quick fix embedded by a repo host.

My laptop is a tool I use every single day and have with me almost all of the time. I do not need internet connectivity to remain productive, which is a huge boon to me when travelling. An IDE that requires constant, reliable connectivity to work is therefore of little use to me.