Thanks for providing your thoughts and votes on this suggestion. I know it's been a while since we last commented on this suggestion and we are sorry to have kept you so long without a clear answer.
We (the Jira Server team) have recently reviewed this suggestion and how it would fit alongside our strategy and other customer priorities. I am afraid we are not planning to invest in more extensive issue hierarchies in Jira. Therefore we decided to close this issue.
While we absolutely understand the logic behind this request, we strongly believe that we should focus on making Jira simpler and easier to use rather then introduce additional complexity on both conceptual and technical level.
Jira as a tool promotes agile approach to project management, where simplicity is key and teams work iteravely to deliver small sections of a project at a time. We strongly believe that current hierarchy of epic, task (story) and subtask supports this approach.
Meanwhile, as Atlassian, we understand that growing teams may require more flexibility. This is why we are investing in Advanced Roadmaps for Jira (formerly known as Portfolio for Jira). Advanced Roadmaps extends Jira hierarchy with the concept of initiative and helps organise and prioritise your team's work to build a realistic roadmap that spans multiple teams and Jira projects.
Also there is a commercial third party plugin available, Structure that provides the ability to create a hierarchy of issues for Jira Server customers.
Since investing in more extensive issue hierarchies in the Jira platform is not aligned with our strategy and roadmap, we will be closing this issue. I understand that our decision may be disappointing, but we also hope that you will appreciate our candid and transparent approach. Please don't hesitate to contact me if you have any questions.
Senior Product Manager, Jira Server