The one for the GTK+2 based LXDE is buried in the wiki and has good detail: http://wiki.lxde.org/en/Roadmap
However, I've already noticed some UI differences between lxqt and LXDE that are making me very nervous. For instance, lxqt does not yet have a proper Panel Settings feature; hopefully the present limited functionality is considered 'interim' but how would we know?

In summary, is there a project-wide process for summarizing the new UI features and goals, including user suggestions and providing a structure for the dev team to work from? I don't consider myself a 'designer', but this team seems like the proper place to document such a process.
TIA, Mike