Ionic 1 with Angular JS 1 or Angular JS 2

My 2 cents,

1) Can I use Angular JS 2 with Ionic version 1 instead of Angular JS 1?

No you cant, Ionic2 is build from ground up for Angular2/Typescript

2) Do companies use Ionic 2 and/or Angular JS 2 as it is not an official release yet?

I dont have any numbers, but I believe Ionic2/Angular2 is too new to have many production apps Yet. But it doesnt mean that ng2/Ionic2 are not out there.

3) What combination is currently used for production apps by companies currently?

As I mentioned in (2), I believe its mostly Angular 1 and Ionic 1 still. Because if you have a fairly big mobile app. Its not easy to migrate to Angular2/Ionic2 straight away. Also since as company point of view its sensible to use a stable framework.

4) Can I use regular JavaScript(not angular) with Ionic 1 or 2?

With Ionic1 you defiantly can , with Ionic2, there is not drop-in solution but there are ways to integrate normal javascript with Ionic2

If you are starting new, I would recommend to go with Angular2/Ionic2 and Typscript. (this is assuming you dont have any app that should go on production in near future). Reason being,

1 - Angular2/Ionic2 is vastly differ from Angular1/Ionic1. So not having a knowledge with version 1 will not effect you on learning Ver2

2 - Angular2/Ionic2 uses component based architecture, which means you app will build as components are its very easy to understand.

3 - Angular2/Ionic2 uses classes, modules etc... So if you have a knowledge in any other OO programming language (E.g ruby, java etc) you'll feel right at home

4 - After some time, there will be more resource for Angular2/Ionic2 than the version 1 and soon version 1 will be obsolete. Tech world time is 10x faster than the normal world time :).