Pitch

It's probably better to keep roadmap linear

When developing some side-projects, often will create many milestones which are basically different directions since they require quite some manpower.

It's really easy to get tempted to try doing multiple features at once and get burned out. Even if you did finish the feature, they don't solve the initial problem well. This is mainly because if you need a few unrelated milestones, it probably means you are not understanding the problem well

Roles

Maintainers care about how well they are doing compared to previous sprints. Features' cost effectiveness are measurable and are needed to keep the motivation going.

Users care about what just got released and what is going to be released soon. Maybe upvote some features they care about

Potential users care about selling points, which I believe should be the metric for feature's cost effectiveness.