Create a status or transition that will automatically close a task after a set time. If, for example, a user submits an idea that we think is already answered, we can provide the answer, then set the status to "Waiting on Confirmation". If the user responds within a week saying their use case is not resolved, we can change the status to a working task. Otherwise, the task will automatically close at the end of the week.
Also send a message to the user x days before the request auto-closes that the request will auto-close if no response is given.