Proposed Regulations were issued for cloud computing and digital transactions; this is an especially important area re: sourcing of income, definitions, etc. especially in light of France and others looking to implement a digital services tax.
Publication 5188 was revised re: FATCA data reporting.
OECD released Peer 2 review reports re: re: BEPS Action 14 (dispute resolution). Interestingly, some US treaties include a MAP provision, although not all are consistent with the minimum standard.