It kills cross-browser compatibility, kills standards (since they're unreachable, undocumented elements that can handle input, interaction and affect other elements.
It's starting to dawn on me what this will really be used for, and I can't say I'm stoked about it. But the article you've linked to seems pretty upbeat about the whole thing.
Even if it will become a standard, it may be complete evil. This concept is quite complicated for regular developer, so some day we'll see petabytes of cryptic, totally undebuggable markup. It should not be done in that way.