Currently Microsoft provides a direct upgrade path from Dynamics AX 2012 to Dynamics 365 for Operations. The code update service at Microsoft Dynamics Lifecycle Services (the collaborative portal for handling updates and upgrades) now accepts a model store document as an input signal, which basically means you could update anything in Dynamics AX 2012 into Dynamics 365 for Operations. But this method works great for the Dynamics AX 2012 R3 CU8 version onwards.
The Reason for this is that the Dynamics AX CTP5 code foundation was predicated on Dynamics AX 2012 R3 CU8, therefore the possibilities for a automatic mixing of code is much higher in versions post-CU8. In our experience, we've started an update out of Dynamics AX 2012 R2 CU7 and successfully updated the code and data.
To read more - http://bit.ly/2ClADlQ
