My current workplace is pretty lean and flexible when it comes to this kind of thing, and we've tried a few different project management solutions over the years. Without fail, the new solution looks great at first glance and feels great as we start using it. Then it gradually becomes annoying and horrible just like the last one, and people start yearning for Jira. The horrible-ness usually comes from straight up bugs, a lack of comprehensive reporting, weak integrations with other tools, and/or a UX that doesn't jive with certain roles/people.

I think it'd be a real challenge to meaningfully compete with Jira. You'd need to not only match its feature set but also be faster than it and less buggy. It seems that being a "not Jira" gets you a good amount of customers off the bat due to how much people loath Jira, but it'll probably take a paradigm shift or a very competent team to overthrow it.