There is another way which enables almost instant loads. Turn off js completely. Try it yourself before you disregard it. It literally turns page loads instant over a regular home connection.
On some wired connections, a network round trip is within user-perceivable 'instant', but for many people on mobile devices, this is very noticeable.
https://hpbn.co/mobile-networks/
Even on the best LTE networks, the 'core network latency' is 40-50ms. 'core network latency' is the latency for getting the packet from the phone to tower to the packet gateway. This is before the packet even goes on the internet. And you need to double it for the round trip. You usually need to double the whole thing for initial DNS lookup.
Best possible latencies for an html page load on excellent LTE connections without prefetching are around 150-200ms. Most users in the world will experience >1s. A United States major city wired connection is not at all representative of what most people experience on a mobile connection.
Just look at Time to First Byte (TTFB); when you pile on SSL negotiation (since most have moved to HTTPS), the advantage is even greater since all AMP pages currently fall under the aegis of Google's domain and all non-AMP pages will require that overhead at first click.
Increasingly, phones are the dominant computing tool accessing Google search results. Optimizing for phone experience is key to serving the largest growing demographic of searchers.
Google doesn't start preloading 50 documents, it loads the top result or 2. Even viewing a hundred amp pages in a month is going to cost you less data than one 10kx10k unoptimized image that a publisher decides to load, which happens a lot. Note that AMP optimizes images too taking into account your device resolution, so it's most likely saving you bytes.
Everything else wastes my bandwidth and I don't care that it is only 100kb, my monthly, effective datacap is about 50MB and I always browser without images.
The "100kb or less" is only about 500 pages preloaded, not accounting for the size of the google webpage itself. I'd rather not have any preload at all.