Try to avoid "Stretch goals" or "Second" Priorities on your Roadmap.
Stuff is either important - in which case it's on the roadmap - or it's not. In which case it's not.
A roadmap is a linear, opinionated sequence of stuff you're going to deliver. Not a universe of possibilities. It should allow you to communicate hard decisions and tradeoffs about what gets done next and what might get pushed back if new priorities are added.
This makes it distinct from a backlog and other tools you might use to triangulate your future workload.