SVG cursors: everything that you need to know about them

If I recall correctly, GTK was initially against cursor-shape (because GTK prefers doing things client side), but is now opening to merging it. But not a high priority. The last discussion I found about it was from 5-6 months ago.

The linked article does a great job explaining the process of creating a theme assuming you have the SVG files. If you are asking how to create SVG files, then just use any vector editor (like Inkscape, for instance). You can find plenty of tutorials on how to create vectors through online video tutorials.