Jira's primary user demographic is by its very nature capable of building a replacement for it.

Build a bare bones system just like Git itself that keeps track of the data and ACLs, and let the silicon valley startup guys make fancy web interfaces and cloud packaging to make it palatable to middle management.

Like Git the core can be moved around and interacted with in the terminal so you're not dependent on any one vendor, and if you don't like any of their GUIs you can just work on the console.

Youtrack

thank you