This is satire, but parallel HTML rendering has untapped potential for both speedup and power savings (as you distribute single-core workload over a larger number of lower-voltage cores).

https://events.static.linuxfound.org/sites/events/files/slid...

(PDF of a Servo talk from 2014)

I wonder if this could be one of ARM Macbook's killer features: a web browser with a Servo-like parallel engine, written for custom silicon with a number of small-ish, low-frequency ARM cores. Or would that be excessive?