There's an argument for being able to get out of someone's blind spot more quickly if you're overtaking on a motorway and going .3mph faster than them, obviously it's a pretty bad one as you may as well stay behind them and go .3 mph slower, but even in that situation cars could be speed limited with a 5mph, 5 second boost you can use once every few minutes at most to satisfy that argument.
There's an argument for being able to get out of someone's blind spot more quickly if you're overtaking on a motorway and going .3mph faster than them, obviously it's a pretty bad one as you may as well stay behind them and go .3 mph slower, but even in that situation cars could be speed limited with a 5mph, 5 second boost you can use once every few minutes at most to satisfy that argument.