[cthulha]

The scale and reliability is the challenge. You could probably hack out a client and server on the weekend, but simulate 10 million concurrent users and every single part of your stack will break.

Also, I suspect that their strategic plan is not about minimising the number of engineers. They may want to be able to set up non-public projects which iterate for years or months before becoming visible: frameworks, app ideas, you name it. Their Fabric platform gives them excellent insights into what people are doing on mobile apps, for example. The kind of insights and understanding they have into personal and aggregate app usage is quite frightening when you realise just how much they have instrumented.