Summer 18: SVG blocked in Lightning Components

You'll want to ask about this over on the Collaboration groups at success.salesforce.com, as well as perhaps logging a bug with Technical Support. I'm not sure how far we'll get with it, but it doesn't hurt to get started on it before the public release.

In the meantime, you can still work around the problem, it's just non-trivial. Using my progressRing example, the source you've linked implies we can still use path, rect, and other SVG elements, so you could copy-paste the actual paths from the resources and convert them to code similar to my design.

Obviously, this will limit your ability to keep up to date with the current SLDS, although I suspect another alternative would be to download the public assets (e.g. "apexpages/slds/latest/assets/icons/utility-sprite/svg/symbols.svg"), parse it manually using a DocumentFragment, find the appropriate path, and then attach it as a child of the SVG tag. I'm going to experiment with this, but please feel free to let me know if you get it working.

Finally, as an absolute fallback, consider using the PNG-based images instead, which you may need to download as a static resource. I hate recommending this, because it's terribly inflexible, but it would at least be a temporary stopgap until you can come up with a more permanent solution.