I have just created a quick test and it worked for me.
added new column managed metadata
set default value in column settings
edited form with nintex forms and published (without changes)
add new item defaults the managed metadata field to my column settings default
Thanks for the advice. I do already have what you proposed working. What I'm looking for is a Nintex solution, not so much a SharePoint solution. I know I can set defaults in SharePoint that point to a static item in my term store. What I was hoping for was a way to use the power of nintex and its ability to use references and variables to populate a more dynamic default value. But from what I can gather this simply isn't possible at this time.
thanks for your reply.
i am also searching for a Solution to Set Default values on Managed Metedata Columns with NINTEX Forms on demand. There are actually no capabilities to Set Default Values on Conditions and rules like for People Picker Columns. It is a missing Feature.