In PlatformUIBundle 1.x, the icon system was based on an icon font. This has several drawbacks (see https://cloudfour.com/thinks/seriously-dont-use-icon-fonts/). Using SVG seems to be a good solution but this can be made in different ways. (dropping inlive SVG, using a sprite + id, using Polymer iron-icon, ...)
Also, this should be analyzed with the Content Type icon system in mind which should be extensible and with various usages of icons in the interface.