3D city models and 3D/4D online GIS are becoming more popular and new technology provides new capacities, yet very few seem to have been used for public engagement in urban planning.
I have heard about MinStad in Gothenburg (Stockholm), and other models from Hamburg, Berlin, and London, but I am not sure if the latter involved public participation.
Below is a link to an undergoing collaborative project in Newcastle-upon-Tyne, hosted by Northumbria University.