We have different definitions for “feeling instant”. Most clicks on HN take well over 2s for me on a 4g connection, and often about half a second even on fast broadband. Sure that feels snappy compared to most websites, but it is still a completely different experience to using an app, or indeed a website that has been designed to eliminate perceptible delays as opposed to making them shorter. These are separate (and sometimes even conflicting) design goals.
Yeah it took over a second to get to this comment page. A lightweight js app could have popped up a modal, I put in my comment, click send, and hide the modal and show a spinner on the bottom right changing to a checkmark when the comment goes through. That's feeling instant, not waiting for the back and forth to a server. The other stories could be lazy loaded in the background as I scroll.
If the delay you are experiencing is caused by your connection, having the data served via a JS worker will not be faster. The additional overhead compared to a pure HTML page will hurt even more.
Sure, if you preload all your sites' content, which I'm sure the users on slow mobile internet with limited volume and those on weak mobile devices will just love. But I don't see that happening in the linked article nor on the demo page.
