Figure 17 in the pdf shows some impressive colorization of grayscale images. It's cool how colors are mapped to the right places. I wish they'd shown more of this.

As impressive as style transfer was when it first came out, it starts to get a little old...

I agree with you that it starts to get a little old; it is not a new topic but there is something else that is really impressive: the result. This paper shows that we are moving forward on a complex topic like colour transfer between images. Compliments for the research work!

It never gets old... Wait for the artist to have this tool. As of now it's only a toy for coders & researchers

True, but a lot of those earlier examples relied on hand-labelled segmented images ("sky", "background", "person" etc.) whereas this could be directly used as an artist's tool without relying on academic data sets.

I'm personally hoping for some open-source code that will allow me to take photographs and game-engine stills and transfer the colour grading to enhance realism.

If all you're interested in is looking at pretty pictures, I can see how you'd say that. But from a research perspective, this area won't be "old" for a long time to come.