When ALPHA 6 asks if you're experiencing any symptoms, select "I'm feeling a little flushed
I went in favor of setting the theme choice early so that I can write a side story specific to each expansion theme.
That does mean that a separate gameplay is needed for each theme, but that there will be personal story elements for that theme that can give a different experience.
The new NPCs that can be encountered can be from any theme, and there are some upcoming combat elements that allow for some more strategy. For the main character, she can only be affected by one expansion type at a time.