Leaving it in master means that import of SCAD and CSG files is supported, otherwise people have got to discover that one needs to install the workbench to have these import filetypes supported.
As easyw-fc says FreeCAD is currently the only software that will allow people who create designs using OpenSCAD to then create STEP versions. I know of a number of people who develop 3D models of components for KiCad do so via OpenSCAD programs and conversion via FreeCAD.
I feel that one of the benefits of the OpenSCAD workbenchs support of SCAD and CSG files, meant that a lot of OpenCascade/OCC bugs got fixed. Sometimes things end of crashing and not be reproducible, where as opening a SCAD/CSG file meant some complicated graphics
operations were repeatable. I know @shoogen got a lot of bugs fixed in the underlying graphics library. We might even benefit if somebody
put together a suite of CSG files that acted as a test case.
If somebody restructured for an addin workbench then maintaing without the need to build FreeCAD would be a benefit.