Overall, I think this is a smart move. A stable API is excellent, but more important than anything is the communication of breakage to your users (e.g. semantic versioning).
I assume you won’t upgrade major versions in the same ROS distro, right? So they won’t have to deal with the hassles of upgrading until they also need to upgrade ROS distros. Do you anticipate maintaining release branches so you can potentially backport bugfixes?