Answer 1

First thing, Angular 2 is not the upgrade of angular 1.
Angular 2 is completely rewritten.
Performance improvements:

Performance improved in Angular 2.0 as compared to Angular 1.x. Bootstrap is now platform specific in angular 2.o. So if application is bootstrap from browser it will call different bootstrap as compare to mobile app. So for browser bootstrap package:angular2/platform/browser.dart is used.

Mobile Support:

Angular 1.x was made for responsive and two way binding app. There was no mobile support. Although there are other libraries which make angular 1.x run on mobile. Angular 2.0 is made keeping in mind mobile oriented architecture. There are libraries i.e. Native script which help mobile Angular 2 mobile development fast. 

TypeScript:

TypeScript(TS) is used heavily in Angular 2. Google currently using DART for coding. DART or TypeScript can be used for Angular 2. Learning TypeScript is very good since other frameworks and libraries i.e. REACTJS is also using TS. Hence if one can learn TS it’s very easily to implement REACTJS and other libraries in project.

If any developer is coming from JAVA, .NET background TypeScript is very easy to learn.

No $Scope in Angular 2:

Angular 2 is not using $scope anymore to glue view and controller. This is one of the biggest problem when you did coding in Angular 1 and then want to try Angular 2 for the project. However if anyone is coming from JAVA, .NET/ background can easily pick up because syntax are more similar to Java.