Well it looks like we finally have an official exam reference:
Upgrade path to MCSA: Windows Server 2016
Start by completing the exams required for MCSA: Windows Server 2012 Certification by June 30, 2016. Then you’ll receive one free exam voucher for Upgrade Exam 743.
MCSA Windows Server 2012
FREE UPGRADE EXAM 743
Upgrading Your Skills to MCSA: Windows Server 2016
MCSA Windows Server 2016