From the Microsoft Dynamics AX Blogs: AX 2012 R2 Upgrades; Project Committed Costs; Kitting; Sales Event Kanbans; EDI Trends
Upgrading to AX2012 R2 from AX 2012: At Yet Another Dynamics AX Blog, self-proclaimed "friendly geek," Tommy Skaue, shares his story about upgrading to AX2012 R2 from AX 2012 (RTM) without Feature Pack, but with CU4 instead. The upgrade is supported for AX2012 with or without Feature Pack, and you need at least CU3 installed.
Because he already had a working environment with AX2012 on CU4, and code in ISV, VAR, CUS and USR, Skaue says he was ready to begin. Skaue says he has a FPK-layer with Data Migration Framework elements, but he's going to remove it before the in-place upgrade.