This actually can be done now. With 2 processes duplicate the first
On second "iron" zero out
Layer >>Bottom Solid Layer
Layer >>Outline Perimeters
Additions >> Skirt Layers
Additions >>Rafter off
Infill >> Infill Percentage
Infill >> Solid Infill Threshold Area
Support >> Support to Aligned
Support >> Infill Percentage
Layer >> First layer height add 0.01mm to ensure it prints after the model top layer.
as for the Extruder > Extrusion Multiplier set this to a small value so very little is extruded.
Infill External Pattern Rotation to 90 deg
Extrusion width to Manual and 0.1
set the Extrusion Multiplier 0.1
Also in the Layer>> Horizontal Outer /Inner Size Compensation set to at least -.5 to keep the nozzle from the edge.
the result should be only top layer showing for the second process. and extrude very little material. This is basically what ironing is doing in cura.
You will also get some warning about about overlapping processes when you print.
preview the iron process first to ensure you only see Top layers don't want to miss anything which should not be printing
Ensure the Model Process is first then the Iron second
So this could be easy to implement just what choices would you want for ironing?
the only thing lacking is monolithic fill
Here is my first try at ironing with S3D (stopped about halfway so you can see a before after on the same part)

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