The emacs startup hack is in it's use of a glibc function called "unexec", which essentially serializes the program's state into a single binary which can later be executed normally.
One of the big downsides (and the reason it became well known) is it's lack of portability, as it requires in-depth knowledge of the system's memory structures.
That would reduce largely the JavaScript runtime size, but not the rendering engine and all the vendored third-party libraries.
On my Arch Linux installation, the node.js package takes about 18.45 MiB on disk. While I'd be glad if the various multiple electron runtimes slimmed down by 10-15 MiB, it wouldn't be much.
There are only so many brain cells on earth, can we stop using them to make javascript things on the desktop slightly less slow? Let's just not use it.
You think that's a waste of brain power? By 2014 humans had collectively spent 200,000 years playing angry birds. That was 3 years ago, and I'm sure pokemon go has at least tripled that record by now. Between than and all other video games we've probably spent in the tens of millions of years button mashing, if not the hundreds.
But yeah lets stop people trying to make JavaScript faster