While waiting for the confirmation email, I read a bit further and already found a hint in the "LibRaw Project Goals and Objectives: Planned improvements" towards my question: How well is the support for my Fujifilm FinePix S200EXR implemented?
The answer seems to be: "not yet complete". Supporting RAF files produced by EXR cameras has a quirk: As the sensor layout has diagonally arranged (octagonal) pixels, the raw files in EXR mode contain two sub pictures with different interpretation, depending on the operation mode.
HR (High Resolution): To optimize resolution, the sub pictures may have to be treated like diagonally interlaced parts of one whole image. I know no software which does that, not even from Fujifilm; the Raw File Converter 3.0 by Silkipix, offered on the Fujifilm website, does not support their S200/S205 EXR RAF format. Possible that Adobe Lightroom knows it, but I don't have that, can't afford it.
SN (Signal/Noise): To limit noise, the result may best be an average of the two sub pictures, like RawTherapee can do since version 5.6.
DR (Dynamic Range): To optimize color depth, the sub pictures may have to be treated like a HDR exposure pair, like HDRMerge does.
I wish you best success finding good implementations...