More than that, the benefits would not be felt. A PWA erases the cost of downloading the JS library, so that startup of the app would be the same as relying on

More than that, the benefits would not be felt. A PWA erases the cost of downloading the JS library, so that startup of the app would be the same as relying on having the same library bundled with the browser. As far as latency goes, browsers won't beat what is already possible in HTML/CSS; or else, they can optimize the engine to match the performance and everyone benefits. That's why browsers' devtool editors are unsurprisingly in HTML/CSS (I believe Chrome/Firefox uses CodeMirror rather than Ace, but it works similarly). Finally, functionality varies from one app to the other. One may want tabs to autocomplete; another may want them to input actual tabs; another, a number of spaces. Some may need multiple cursors, and some may need the editor's algorithms to not be too slow when the data to edit is compiled text (say, a single-line 100k minified JS file can crush the performance of your text editor if its string data structure is not ready). There are no outstanding benefits to having a library be bundled in the browser.