The biggest problem with this is that it requires uniqueness to be traded for error tolerance. People are going to have different typing styles depending on the

The biggest problem with this is that it requires uniqueness to be traded for error tolerance. People are going to have different typing styles depending on their mental and physical state, and their typing styles will change over time. In addition, while the space of possible typing signatures is very large, the space of actual typing signatures is much smaller. So we simultaneously have to assign each person a blob of signature space which is big enough that it can positively identify them regardless of whether they've had their morning coffee (or, god help them, they cut their finger or break their arm), and small enough that we don't have so much signature overlap as to make the system useless. In either case everybody will have to have a fallback password in case their stride is off one day. If the system works well, then that password will be rarely used. A rarely used password is harder to remember than a regularly used one, so people will choose weak passwords for the fallback. So the only way that this system has any chance of working without grossly compromising everyone's security, is if it barely ever positively identifies anyone. Of course, even if it did work perfectly, it would be the equivalent of having the same password everywhere. In that case, why not just memorize one strong password?