I modified the working of Arch WB so now, on creating a window or a rebar, the external references of the base sketch are no longer removed. Instead, the window/rebar is not attached to the original wall/structure anymore, but to a new wall or structure that uses the former as base object.
So far this seems to work nicely. It will inflate a bit the model (one more object everytime you create a window), but I think it will stay manageable, and it is much more freecadish. And after all, one day or another, we will have assembly!