I'd like a way for users to submit feature requests

You can add a topic like this one in your community. End-users can go there to add feature requests and describe their use cases. Other users can comment on the requests and vote for them. Product managers can review them and provide feedback.

If you have an idea for a Help Center feature, you can submit it to Zendesk here: https://support.zendesk.com/forums/1848.