I'm having trouble changing my "Assign to" Tasks to Flexi Tasks. The main problem consists to add fields to the content type of the Workflow Tasks list. With "Assign to" Task there is no problem because you can edit on the same form the content type. With the "Flexi Task" I've tried to add a new content type on site level which inherits from Nintex Workflow Multi Outcome Task but the new field doesn't show up in the task.
Is there a way beside Infopath or Nintex forms to add a field to a flexi task?
I'd like to see this feature too but right now you can't add any custom metadata to a flexi task action in design mode. You can use a customized content type and have the user enter the custom metadata when editing the task but in my scenario this is too late and messing around with task metadata after it has been created makes workflow unstable in many cases.
There is a feature request on user voice Ability to Set Task Properties via FlexiTask Action – Customer Feedback for Nintex
Maybe you want to add your votes to the feature too to make it more visible to Nintex.