It's a plugin - meaning that we limit the users to using a subset of browsers (those with supported plugins) and forcing them to upgrade it when we want to use the latest features. This is NO worse than flash, it's just you write the apps in C/C++/Go rather than ActionScript.
I don't see the benefit; all I see is another Flash/Silverlight wannabe that puts more reliance on the user understanding their system/installed programs. This is not the future.