As the WeBWorK code has been updated and modernized some of the approaches used for these types of questions are no longer practical to maintain. For one thing, having a WeBWorK problem send emails is no longer sustainable, so it's unlikely that that functionality will come back.
This thread already mentions essay answers as an option for collecting free-entry responses, though these would not be anonymous.
Anonymous surveys were never a core feature of WeBWorK, so it's not something that will likely see any new development in the near future. I would strongly recommend looking for a tool that is designed for this purpose. If your institution has a learning management system (e.g. Blackboard, Moodle, D2L Brightspace, Canvas), then you can use the survey feature that is built in. If not, there are commercial tools that offer a certain amount of surveys at no charge (e.g. surveymonkey) which may serve your purpose. Just be careful about what information you collect if you are using a commercial website, so as not to run afoul of your privacy office.