I'm building such a thing at https://hillview.cz/ , the content is heavily centered around my city, but i'm open to any contributors. The whole thing started as a tool to help track down what you're looking at from views around the city. At that time, i wasn't aware of Panoramax (and a few other projects), but in the end, everything seems to be converging into one federated "geocommuns" anyway...
Any plans to make it global?
I think there is a lot of people who document (urban) landscape and would like to place their photos into map together with the view vector.
OldMapsOnline has a lot of georeferenced old map layers from around the world…