That's the concern I have; not that it's going through the WICG, but that whatever process it's going through, this blog post sound like Google announcing user-facing shipment of a feature that hasn't finished its standardization process.
We've already been through this before with Web Bluetooth and the Shadow DOM specification. Once Chrome turns a feature on for end users, it is effectively standardized -- it is very difficult to justify changing or evolving a spec once real sites on the actual web have already started to rely on it. Again, look at Shadow DOM as a good example of why this is a problem.
I'd feel more comfortable about this process if there was some clarification that this is an intent to ship only behind a flag, or an intent to ship only to dev/beta versions of Chrome.