Renaming symbols, and minification in general, is not really "necessary", it's just something people do to extract a few % more of performance. If they had that file format, they'd still have exactly the same reasons to rename symbols, so they'd still do it.
After all, if people cared about leaving their files readable, they'd just publish the non-minified version as well. Those who don't, won't avoid renaming either.
I agree that renaming symbols would still save a few more bytes, but I still think that with the right file format, symbol renaming and mangling would become an insignificant, unnecessary micro-optimization.
But that should only be tested in practice, so ... :)
This seems backwards. If I have JS source and the identifiers take up 10% of it, then symbol renaming and mangling can shrink my code size by something less than 10%.
If we shrink that other 90%, so that the formerly 10% is now 80%, renaming becomes more attractive.
This doesn't hold if people have a fixed problem with a fixed solution and fixed constraints... but problems and solutions grow.
After all, if people cared about leaving their files readable, they'd just publish the non-minified version as well. Those who don't, won't avoid renaming either.