There are OGC web service providers that support custom URL parameters.
Eg.: it is possible to include parameters in the SQL of an 'SQL View' layer in GeoServer. The parameters can be passed as query parameter in the request URL: &viewparams=param1:value1;param2:value2... (Such a parametric WMS request make life way easier when ther is a good SQL)
It would be handy if WFS/WMS readers support custom URL query string parameters like in the HTTPCaller.
Now I have to use the 'manual WMS' (HTTPCaller->RasterReplacer->CoordinateSystemSetter->RasterGeoreferencer) to benefit from this functionality.