Google isn't a fan of non-standard approaches to fast-charging Android phones over USB-C, and it's bent on having manufacturers fall in line. Its newest Android Compatibility Definition document (for Android Nougat) now says it's "strongly recommended" that device makers don't support proprietary charging technology that modifies voltages beyond standard levels, or otherwise creates "interoperability issues" with standard USB charging. In other words, tech like Qualcomm's Quick Charge 3.0 is likely considered naughty. On top of that, the company warns that later versions of Android might even require full interoperability with standard chargers.
This doesn't mean that you won't see fast charging. Remember, both of Google's Pixel phones can top up quickly. However, it's evident that Google would like to fulfill USB-C's promise of cables and chargers that always work together. It doesn't like the idea that you might have to carry a specific charger for your phone to work as expected, or that a flaky cable might fry your charger, phone or both. The company might never force vendors to drop their preferred fast charging standards, but it certainly won't look kindly on them.