I would say the same thing for using a webcam in the browser or accessing the filesystem. But yet everyone use it today and a world without it is unimaginable.
Wrapping functionality with the right security is key, but I browsers in general is already doing a good job in that regard IMO.
Yes, but I really don't see the usecase for letting something potentially remote and untrusted to a serial device. How many people do actually need that? (Limited) filesystem access for web applications is also kind of dubious, outside of the trusty upload form.