Having instantly loading non-SPA pages is possible when they're prefetched. For instance, the UI Drafter's docs are sequential pages, so we prefetch the next page in the flow.
The prefetched pages stay for at least 5 minutes in Chrome's cache, as Addy Osmani explains in his article:
…prefetch requests are maintained in the unspecified net-stack cache for at least 5 minutes regardless of the cachability of the resource.
Option 1: <link> tag
Add link to the head:
<head> <link rel="prefetch" href="/the-next-page">
Option 2: Link response header
Link: </the-next-page>; rel="prefetch"