First class off line experience is a must. As more and more of us move to remote only (huzzah!) you can't always expect to have connection. Some of the best, most productive environments are exactly productive because they have no Internet connection. Make this seamless. While using git is desirable to some extent, making it just work from the browser whether online or not IMO is way more important.

Make it fast. Neither the developers nor QA cares about anything else but the meat. JIRA Cloud is atrocious for basically using a single page web app loaded per ticket. No need for that, absolutely not. I will be much happier if each page loads 60ms even if the price is an occasional reload. Some people have forgotten how much unnecessary junk is loaded for a tiny bit of information. I saw some of your intro gifs included animations. Drop that. Noone needs that. Seriously. We. are. not. here. for. the. bling.

One field that must be required and I have yet to see a bug tracker putting it in the spotlight: URL. If you are working with a web app, almost no bugs can exist without an URL.

Integrate with a screenshot / screencast extension. It should be natural to just show what's wrong. Right now, the workflow is: record the reproduction steps, save it off line (or google cloud at best) and insert. This is too much work. Since we have a URL, a button should open that URL and start recording and end of recording should just immediately insert it into the bugtracker and the ticket. (These movies are not likely to be atrociously big since they are can be very low frame rate and they compress real well.) Same for screenshot.

Do not have many required fields but do allow for optional ones. As Spolsky says, having too many required fields make filing bugs atrocious but not having certain fields make the life of project managers hard. Let the programmers/QA people file tickets quick and easy and let PMs organize.

If you don't have Slack integration, these days, you are dead.

And if I were dreaming... something neither Atlassian nor Google can do properly: make multiple logins just work. If I have authorized with email address A which can access the tickets of client A and also authorized with email address B which can access the tickets of client B then don't make me manually switch accounts! If I open a team A ticket, the app should be able to pick the account which can work with them and ask for a decision only of there are multiple. Freelancers will bless your name for ever. How come Google wants me to pick an account when I click on a meet and can't pick the one automatically the one I am logged in with that has access?? Raskin is spinning in his grave.