> Am I wrong for presuming that the people who would most care about GitHub's public roadmap probably aren't even GitHub users?

I think so. I'm a GitHub user and I like being able to view their roadmap.

Think about it this way. GitHub is a giant piece of software that developers use. Software changes, and developers are particularly sensitive to this. We're constantly fixing bugs and factoring code to support dependency shifts (or choosing to snapshot ourselves at some preestablished point of stability).

Given our sensitivity to change and how important GitHub's product is to our productivity it's crucial that we're not hit with surprises. A properly communicated roadmap helps avoid that -- thought admittedly it does take some work on our part as customers to parse it. That said this is no different than reading release notes and documentation for the software and libraries we use elsewhere in our day to day.