As already mentioned, this will be very handy for support contexts and I particularly like the suggestions from @packman regarding custom user fields.
Is adding form templates to groups also on the roadmap (or could it be)? Where messaging a group is used for private support, this will be especially useful for front-loading questions before a member of staff arrives.
Depending on the visibility of the custom field, this could have privacy implications. For example, the user might choose to share the information via a form template in a private category but not want to share that information with the wider community via their profile.
Depending on the nature of the information, it might also have one value that is appropriate for their profile and/or most forms but they might want to provide a different value in a particular instance.
I like the idea of filling in the form from those fields and being able to update the fields if the entered values differ but perhaps that should be a prompt. This is a really quick and dirty mock-up but maybe something along these lines after creating the topic (only if a value differs and possibly only if non-empty):
