Thanks for your feedback. TestRail actually already allows you to link test cases to external requirements via the References field. The References field for test cases allows you to enter one or multiple requirement IDs and TestRail would also automatically link those IDs to your external system when you configure the integration URLs for this (if your requirements are stored in a web-based system):
You could also import the requirement IDs as part of test cases via TestRail’s import feature or even automatically update your test cases via TestRail’s API.
The only missing piece at the moment would be the traceability report. We would like to add this to TestRail but we don’t currently have a time frame for this. We want to concentrate on reporting improvements this year and such a traceability report is certainly something that would be part of the enhancements we are looking into. You could already write a custom report for this in the meantime or we could help with this if you prefer that.
Thanks and just let me know if you have any further questions about this.