To get back to the original topic. I think roadmaps are a bit of a thing with openHAB. Mainly because the current structure is a collaboration of individuals. Meaning only if someone contributes something there will be something new and this is hard to plan because its on a totally voluntary basis.
That having said there is a project wide board for openHAB 3 to track progress. It’s probably not completely up-to-date or complete but gives an idea. https://github.com/orgs/openhab/projects/3
(This board was previously not open, but it is now)
For addons specifically we track milestones. For example you can see what is already merged and what will be in the next release: https://github.com/openhab/openhab-addons/milestones