I've printed gallery quality prints from sRGB (online and at home), and nobody gives a crap.
Of course no one cares if you print something for your house or a friend and the color is slightly off. But in some industries something like that can cost you a big client and a lot of money.
[0] The difference can be quite dramatic, even without a professional monitor.
Why would I need something in GIMP whose effect can only be seen on paper, except as some kind of Export ... format?
Suppose I have a properly calibrated monitor, yadda yadda, I should be seeing good colors on the screen as I'm editing. When I'm done, good colors on paper can only be seen after the data passes through a professional printer provided its RGB values have been properly massaged into CMYK values. So it has nothing to do with interactive image editing.
It's almost entirely "off topic" for GIMP.
The problem: https://upload.wikimedia.org/wikipedia/commons/1/1e/CIE1931x...
Colors in one colorspace may not have a representation in another. If you do all your editing in RGB and then try and convert at the end, you restrict yourself to the set of colors available in both. To get print colors that are accurate to a provided spec, you need to work in the target colorspace directly, with an editor that will approximate the colors on your sRGB monitor as best it can so you can see what you're doing.