From what I saw on EDM/2 WPS articles every one points that WPS is a set of classes constructed over SOM.
The classes of Warp 4 with their hierarchy are:
There is also an API that has WPS related functions like WinCreateObject and a lot more, but those are part of the Presentation Manager API (I think).
My next steps is trying to understand more about WPS to solve this questions:
1) If we have an open source replacement for all this WPS Classes can we say that we have a 100% WorkplaceShell open source clone?
2) What will be the effort of replacing all this classes based on what it had been done in the XWorkplace project.?