[fevangelou]

Once ad agencies/networks take note of this feature, they will 100% start using it and abusing it.

We're already seeing some ad networks using initialization scripts to bootstrap their ad setup, with dynamically constructed secondary scripts that have a high fetchpriority (so they supposedly load faster than others).

For reference, modern news/media sites may load multiple ad networks (3-4 on average perhaps) in order to optimize ad performance (revenue) or inject different kinds of ads or sponsored content. If we take Google's Ad Manager (or similar) as the base network to serve ads (own or third-party), many times we see additional networks like AdSense, Taboola, Outbrain, Vidverto (to name a few) or other local ad networks that do some sort of header bidding, ad injection, sponsored content display, in-read ads/videos and so on.

I don't see why some won't abuse this spec to force-inject their stuff earlier than other ad networks and of course at the expense of a site's performance...