I'm on 7.1.8. I have an activity where I need to 'execute' a Section and have it return the Resulting HTML as a string. The OOTB GetSectionHtml activity is close, but I'd need to modify it to return the stream property.
Have you tried "Property-set-stream". I think that should solve it. If it doesn't take the section name as the input then create a fragment rule and include the section inside that.
Let me know if this helps.