Google shows these URLs as the most prominent search results for "kdenlive roadmap", but both of them are rather outdated.
https://community.kde.org/Kdenlive/Roadmap
https://community.kde.org/Kdenlive/Deve ... ng_Roadmap

The first also links to Kanboard at https://phabricator.kde.org/project/profile/40/ but while there might be some information about what is currently happening, there is no roadmap.

Are there plans to update the roadmap?

I would say today's roadmap is in invent wiki:
https://invent.kde.org/multimedia/kdenl ... /dev/Ideas
That's very sure we need to clean up our obsolete docs everywhere, sorry for that misleading mess!

Sounds like this should replace the old roadmap. Most of these old points will probably have been implemented already.