I was looking to create a similar discussion, so thought I would add it to yours.
We currently have some basic CSI reporting setup in Workfront. It is a set of custom fields on a custom form which represent questions which we store a numerical response to. The custom form is attached as an Issue with an 'Other' topic type. We then do various reporting on the values of the custom fields. We do not have regular users/customers entering the data. The data entry is done by specific managers who then use the reports that Workfront generates. If you want to have a look, I previously posted a screenshot at https://community.workfront.com/p/fo/st/post=1698#p1698
We are looking to extend CSI reporting to end users (including customers). What we have setup is not very user-friendly and will get complex to maintain and report on if we want to expand the use of it. Customers also don't (currently) have any access to Workfront.
I am keen to know if other customers do use Workfront for CSI reporting, or what other systems you use, and if so - whether you have a way to report on it in relation to Workfront data and/or push results back into Workfront somehow.