I agree that making workflows configurable seems like a better choice than extending the existing workflow with a new option: NEXT.
Currently, you have TODO/DOING and LATER/NOW, and you have to decide which. Why not be able to define multiple workflows where each key word is considered a marker (a term used in plugins). Then clicking these marker words simply cycles through them. This would itself be more conducive to a better version of the Kanban plugin. Such a plugin would be turned on for a page and it would understand what columns should exist based on the existence of tasks and their markers.