A new white paper released by Discover Technologies addresses the downstream effect a SharePoint environment upgrade can have on workflows.
Essentially, the upshot is really the difference between K2 blackpearl and other, SharePoint-based workflow solutions like Nintex Workflow: K2 blackpearl has its own workflow engine, and does not require SharePoint to operate. Other, SharePoint-dependent offerings (including Nintex) were faced with a major dilemma when Microsoft introduced Workflow Manager 1.0 (WM), because WM moves the workflow engine OUT of SharePoint, and there is no upgrade path to WM-based workflows. Microsoft did leave the legacy 2010 workflow engine in SharePoint 2013, allowing dependent workflows to run with upgraded content — albeit sans 2013 features. The only way Nintex and other workflow users will be able to take advantage of WM and its feature set (which is incomplete, by the way) is to rewrite their workflows. And if Microsoft doesn’t leave the 2010 engine in SharePoint 2016, those processes will have to be refactored sooner rather than later.