Have you tried pre selecting groups to add to your Smart List step before you get to the Flow?
That's the only way you can use random sample within the Flow.
Setup a separate Random Sample operation to take the target list and break it up into separate static lists which are randomly selected ahead of time.
With the way things are currently set up, these steps couldn't be achieved within the Smart List stage; only in Flow.
Ex: a trigger campaign requires a waiting period before SF will have updated the other fields used as filters, so this is additional segmentation is done using a Member of Smart List choice in Flow.
Ex: a trigger campaign uses a SF field in Flow that determines send time optimization (this is achieved through a series of wait steps and constraints using different values of the SF field.
Can segments be used for testing (i.e. dynamic content)? I could use segments to randomize our entire database and test different subjects and copy that way, but will I be able to track the results?
Also, how would I then test extensive design changes (HTML) beyond just using different images within dynamic content?