I'm not sure what you're getting at?
The browser landscape today is composed of practically just one browser: Chrome. It is easier than ever to get browsers (read: Chrome) to implement different rendering schemes based on identifiers or descriptors provided by web devs.
Supporting the latest and greatest is a great marketing ploy, browsers (read: Chrome) are incentivized to support them. Browsers that don't will be forced to support them lest they become even further irrelevant.
Quirks Mode happened, Quirks Mode V2 can happen.