1. In the browser, even if you can't allow raw machine code (for security reasons), you could at least compile your V8 bytecode into LLVM IR and then into WebAssembly. It would make front end code way faster running (b/c of compiler optimizations on the ENTIRE code base) and loading (smaller sizes, probably). 2. On the back end, you can compile straight to machine code instead of V8 compiling stuff at runtime. It would certainly be faster, as that compilation is happening in advance versus at runtime.
There has to be some reason why this isn't being done. Perhaps the information at runtime is required, and a proper compiler would be too slow? Maybe there would be no major performance benefit? I could be wrong about the above two ideas. The V8 team has a ton of really smart people, so I can't imagine they haven't already considered this.