This feature is more aimed towards folks who are just beginning to peek at the assembly output out of curiosity, rather than the experts who are already familliar with most of the mnemonics.
For example in this thread, an embedded reference on operand order could have saved a bunch of time and effort.
But yes, this could be an external tool. It just seems straightforward enough to offer within Julia though an additional flag.
Good point about looking at the llvm output. I previously assumed that the llvm code is further refined before becoming machine code, but I now see the optimized form is displayed by default.