It is good new for yii developers by May 3, 2013 from Yiiframework.com that Yii 2 is coming with great new features but the bad thing is that they would not be able to upgrade their current projects to this version. As I look at the code, I found.
It is still in development, right-now it can’t be used in development of projects. It has more concentration to Namespace, scope etc. It is good that Yii 2 is coming with Build Tools.
Yii 2 directory structure
app/ a ready-to-use application built on Yii 2
build/ internally used build tools
framework/ framework source files
tests/ tests of the core framework
Yii 2 requirement