@RawConvert Thanks! for sharing your experiences with commercial printers. Mine have been a bit different. Of the four or five commercial printing places I’ve looked at, two supplied soft proofing profiles but requested that the image file not be converted to the printer profile, and stated that they only use perceptual intent to make the conversion for printing. The other places were local printers who clearly don’t have much of a clue (well, one didn’t know what AdobeRGB was, so that was the end of that conversation, and the other turned my sample black and white image into shades of purple and white and then said that was “normal” . . . ).
Being able (or rather required) to make the conversion yourself for standard prints that’s nice! it means you can choose the conversion intent, plus of course make whatever corrections you want to make.
I do soft proof most of the images I process to a couple of different printer profiles, just as a check to make sure I’m producing printable colors, and almost always I use relative colorimetric intent. Some day I hope to actually start making prints.
As far as the art papers go, these papers often have a very limited dynamic range with a fairly light black point. I can see why a printing establishment would prefer to make these conversions themselves, just to keep the customer from going nuts dealing with the mismatched black points.
GIMP 2.9 has a very nice framework for soft proofing. Unfortunately there are problems with LCMS soft proofing that might, or might not, affect results depending on the image precision and the TRC of the source color space (and especially if you are using my patched version of GIMP to edit floating point linear gamma images). These LCMS limitations affect all software that uses LCMS for soft proofing, more or less depending on the allowed workflows and whatever compensating workarounds the image editor/raw processor might provide.
From what I can tell through testing, PhotoFlow (the linear gamma branch, I’m not sure about stable) has pretty good workarounds for most of the LCMS limitations. I’m not sure what the RawTherapee processing pipeline really is, so I’m not sure whether RT even allows to replicate the problematic situations that affect some (but not all) workflows using GIMP (the same issues also affect Krita).