left-pad was released under WTFPL, so in this particular case there'd be no legal barriers to it. (And I'd assume that, for any libraries with a restrictive enough license, it wouldn't be a hard sell on TC39's part -- if they put out an announcement that they were going to do that, I'd go panning for street cred, and I wouldn't be the only one.)
An alternative could be to pull all this stuff together into one big bucket of Legos and package it with a code analysis tool at the beginning of your build process to strip out everything you don't need from the bucket... but I'd guess that's either already been done or a stupid idea for reasons I don't know yet.
