That's amazing!
How's it compare to a minimised SVG, gzipped, in practical terms? I see projects elsewhere just blithely using SVG or SVGZ. (or, in horrifying cases, multiple sizes for hundreds or thousands of icons.) Perhaps this is a thing that would be suitable to wider use if it can get good lib support.
Optimization tools do exist [1] to simplify the tree but they can do only so much good[0]. I think this format, built with optimality might be a solution.
[0]: Anecdotal. I once had to edit ~20 icons. The client had provided SVGs because they'd somehow lost the original AI files. When I imported them in Sketch 3, the nesting, masks, and transforms applied were absolutely horrifying! I had to optimize the icons using [1], which did remove the masks and transforms, but in the end I had to manually edit SVG's XML source to fix nestings. sigh.