Personalization could include showing the same cached content to many people. The personalization here could refer to which content is served from the CDN to which users.
I can’t imagine the number of editors is that large? Are we talking about hundreds or thousands? Taking a look at the site there can’t be that many users that need this low latency preview capability.
That's not the problem.
The main requirement is to allow editors to preview their changes without having to wait multiple seconds due to caching refresh cycles.