Now I'm thinking I should build a better Jira where the basic unit of everything is a range instead of a number. I wonder how long that would take me.

If you’re looking to capture all of JIRA’s features, it would take you a very long time. Duplicating their extensive automation capabilities is a massive project.

If you ever get around to that, let me know. JIRA really is best in class and I want to shove it into a very tiny, very lonely box before tossing it into the deepest part of the ocean I can find.

The area of statistically sane software for regular users is so underexploited that there are many instances of X you can plug into "X but with ranges instead of numbers" and carve out a niche for yourself.

I myself am hoping someone will pick up X=spreadsheets at some point soon.

You’re looking for causal.app for that, and it’s as good as it sounds.