And not only. From the paper: "WebAssembly is an abstraction over modern hardware, making it language-, hardware-, and platform-independent, with use cases beyond just the Web". It could have some use in the embedded space, for securely embedding code. Java is sometimes used to sandbox code, if the WA compiler is slim enough it could be an alternative. A big difference is of course the libraries, which are not in the WA scope. But for some embedded use cases this is not a blocker: the API is there at the C level, one just need to expose it to the WA runtime (which could be automated, see SWIG and the like). A secure format, with some strong backers and high performance open source implementations has a lot of potential. I'm very curious about the footprint of the loader/compiler/runtime: it should be ok for most Linux embedded systems, but how low-end could it go as a secure ISA agnostic code distribution system?
For your second point, JavaScript is also sandboxed. On principle, there is no reason that in time the API offered to JS today won't become available to the WA runtime in the future --- although I've no idea if there's any actual work along those lines, I don't follow web front-end tech too closely.