Google can do pretty much whatever it wants when it's the only player in the space. It certainly hasn't been shy about doing things outside of a standards body. Sure, it's open source, but can you meaningfully influence the direction of the project? If you decide to fork and deviate from what stock Chrome is doing, you're apt to be locked out similarly to sites that don't support Firefox or Safari.

It looks pretty similar to what MS was doing with IE, just with a dash of "here you can skin this thing". The biggest differences being that Google has a strong interest in ensuring the web is the app platform of choice, rather than a desktop OS. On the other hand, Google needs to sell targeted ads, so it's unlikely to be the standard bearer for web privacy.

If Google has a monopoly on the rendering engine, who decides what the future of web rendering looks like? Google, and nobody else.