False... the first official alpha was released... so there will be some time until it is final .
Even angularJS is still in alpha phase.
If someone will use this in production .... good night
There will be a guide to transform your ionic app to an ionic2 app.
Before starting ionic2 everybody should make experiences with pure typescript...
Back to topic.
It depends how your app will be used. If you need offline synchronization out of the box --> use couchDB/pouchDB as dbs. If this is not necessary. but you have thousands of users parallel using your app. or you need to write many data --> use a NoSQL dbs like mongodb (it plays well with nodejs, but can be used with many script/programming languages). If you only want to play around and it is an app for a small range of users you can use everything. Even PHP and MySQL.
But keep in mind... you can use the fastest dbs and programming language ... if your code sucks --> your backend will be crap ^^