Developers are quite conservative of their environment, but a cloud IDE could be awesome.
I want to write code on a 2 lb MacBook, with continuous build-as-you-type in the cloud on a fleet of Xeons that have larger CPU caches than my entire project.
Have 5, 50, 500 tests that need to run? Run them all in parallel continuously and get immediate red/green feedback in your IDE. Behind the scenes Lambda takes horizontal scaling from minutes/seconds down to milliseconds, so go radically horizontal.
I want my editor, exactly as I left it, down to the open tabs and cursor position, on any machine. And pair-programming Google docs simultaneous-edit style, without either party giving up the ability to run/debug the software on their own.
What if the FaaS/Lambda lifecycle management was tightly integrated in the IDE? Working on, testing, versioning and publishing a function could be re-imagined in a non-file centric way.