Malte,
Are you working with the current survey package for OpenACS 4.6? Survey sections are objects in there, they just are not exposed, and the hard work of writing the rules is not done.
Do you have a list of requirements that your branching work will fulfill? I know that for IMS support, there is a concept of sequencing which may, or may not mean the same thing as branching :) Specifically, sequencing deals with repeating a question, either a number of times, or based on a response. Another aspect mentioned is the sequencing of questions from a larger pool of questions. For example, a test may contain 50 questions randomly choosen from a list of 100.
I thought workflow might be an interesting way to try to sequence objects. Besides that another useful feature I noticed was the templating wizard. It shows progress along a list of tasks. It requires your code to keep track of the state, so an ideal solution would probably be a mix of workflow and the wizard.
Anyway, since I can't actually work on this, I hope this information helps you.
