It only takes 33 bits of information to identify 1 person out of 7 billion. How many bits did you lose just by talking about neural networks in that one sentence? How many bits did you lose from the timing/time zone of your comment? By the language of your comment?
Which means anyone who does this will probably have made themselves unique, or - I guess- at least narrow down the scope of possible users more than the typing speed would do.
There are hardened browsers that will make the script wait for a while to get the key events. That seems like the right solution; most people using controlled enterprise apps don't have to deal with huge amounts of input lag, while people that are paranoid won't be profiled by their typing cadence.
uhh, probably 2 or 3 at most? Given the demographics of Hacker News (technical background, mostly American), probably half the site have the attributes you have listed.