The project "WUProp@home" is missing from BM's "add project"
It is listed here https://boinc.berkeley.edu/wiki/Project_list
How does one go about getting a project added so it shows up when the manager does an RPC "get_all_project_list" call?

There is a contact number at this location for adding https://boinc.berkeley.edu/projects.php but I suspect that does not get onto the BM RPC call database and someone at the project needs to make the request in any event.

There is a file "all_projects_list.xml" in your BOINC data directory which defines the entries shown on the 'attach to project' wizard in BOINC Manager.

The same list also drives the display at https://boinc.berkeley.edu/projects.php - the modern version of the wiki page you reference.

As the Wiki says, "This page is no longer kept up to date". The replacement list is maintained by David Anderson personally. He prefers to be contacted by email.