I think it would be a good idea to incorporate a permission within a category where a user can create topics and only see the topics he or she created. I saw this was already suggestion over 4 years ago so I thought maybe there would be more of an interest.
This can help with moderator applications or whatever without having to use a service such as Google Forms to keep everything isolated, my use case but I guess it can differ among other forums admins.
Have you considered having users send a PM to a group for this? Users who send a PM to a group will only be able to see the topics they have created. Members of the group the PMs are sent to will be able to see all messages in the group inbox. This is how we handle customer support at Discourse.