NaCl does not allow direct manipulation of the DOM or provide other JavaScript APIs like canvas. NaCl provides alternative ways of getting things done like pp::Graphics2D, but it is not meant for DHTML. Dash, on the other hand, provides access to JavaScript APIs.
I think that browser "assembly" code, like Dash, would have to support this, particularly if it is meant to be an alternative to compiling to JavaScript.
This is not CSRF. It uses an iframe containing a pre-filled hacker news submission form effectively causing the user to upvote the already existing story.
It could be argued that hacker news should implement frame busting for additional security, but I don't think it is a huge concern for this site.
Square certainly is not going to hurt Visa. The whole point behind Square is to make it easier for individuals and small businesses to accept credit card payments from which Visa naturally takes a cut (when their cards are being used).
This doesn't mean that the technology isn't disruptive. Obviously, it is too early to tell for sure one way or the other, but I could imagine Square clearing the way for a new and potentially huge market for smart phones with built-in credit card readers. Given this scenario, Square would most likely not be profiting off of the technology, since I doubt smart phone manufactures would license a credit card reader from them, but that doesn't mean that the technology that Square is introducing isn't disruptive.
In many ways it would be safer and more convenient for people to use credit cards for their personal transactions instead of cash. Credit card companies generally do a good job of mitigating fraud despite the ease of using stolen and copied cards.
There are a lot of reasons the technology might fail too of course. For example, people might prefer the anonymity cash provides. We'll have to wait and see, but to argue that the technology isn't disruptive simply because an established player like Visa stands to benefit seems silly.
It's not perfect, but in my opinion it is certainly the best free option available. I have never used ViEmu, so I can't compare it to that.