YoyoGames have just announced the public launch of GameMaker Studio 2 beta. The beta is slot based and according to posters on reddit all of the initial beta slots have now been claimed. According to their FAQ they will be releasing more beta slots over time:
It says there are no slots left for the beta, how can I take part?
We will be opening up more slots over the beta period, please keep checking back or follow us on social media
The posted expected pricing on the beta page, showing first that their is no subscription model available and that GameMaker Studio 2 will be $100 USD with additional platforms costing between $150USD and $400USD.
In regards to upgrading, from the FAQ:
Can I upgrade from GameMaker: Studio?
Yes you can - for a limited time existing Professional users and module holders will get 40% off the equivalent Studio 2 product and Master Collection users will get 50% off each product. Please visit www.yoyogames.com/get2 for more information.
They have also posted a roadmap showing when you should expect additional functionality to be added to the beta:
Oddly missing from the announcement and FAQ is a list of new features and functionality over the current 1.4 edition of GameMaker. There is however a list of the new functions available.