As I argued previously, abuse doesn’t necessarily need to done through bot accounts, unique human accounts can be used, so even if you can get a PoUH it doesn’t solve the abuse:
Nymi solves the problem that person A can’t pretend to be person B, it’s not made to prevent fake human identities. The heart beat is recorded by a sensor and in the resulting signal a pattern is recognized that is unique for every human. Nowhere it is stated that Nymi has an algorithm that can discern a real human heartbeat signal from a fake one. It’s probably relatively easy to record a real heart beat, morph it a little bit, and voila, you have a new unique signal that is 100% human-like. Save this signal and you now have a unique ID for a bot. Nymi isn’t made to solve this particular problem.