As from todayyou are able to download System Center 2012 R2, Windows 8.1, Windows Server 2012 R2 as you have access to the Microsoft Developer Network, Volume License site, Microsoft Partner Network and on the TechNet Evaluation website.
The last couple of months Microsoft worked hard to also upgrade their Windows Intune cloud service to the next version, looking at the schedule posted here, this process must be almost ready.
Congratz with the new version and have fun upgrading your environments! 🙂