If this becomes an open-source library that you can integrate into your app's own JavaScript blob and obfuscate, it can become ridiculously difficult to detect and distinguish from regular JavaScript processing in a sufficiently complex web app, as long as the actual mining is throttled to a reasonably low rate.
This seems like something that will inevitably be everywhere and displace some use cases for advertising, and could possibly even replace it entirely eventually. I personally see it as the lesser of two evils, as long as apps don't try to run miners at full throttle and thereby provide a horrible user experience, and instead operate it at say 95% idle and only when I'm actively using the app. Although in practice I realize this is almost impossible to identify and enforce.
I'd much rather offer some limited amount of compute on my devices to support content creation on the web and than to offer my privacy and be subjected to subliminal mind tricks 24/7 as I'm forced to in the status quo.