Docs.rs already has support for deprioritizing large projects that could impact the build queue! The docs.rs team monitors the queue, and when we notice a big project causing disruptions we set the default priority for those crates to be -1.
The current way projects are added to the "deprioritized list" is manual: the docs.rs team gets alerts when the build queue gets too long, and if we determine the project is using too many resources we add the relevant rules to the list.
We're using this approach rather than an algorithm to automatically deprioritize to avoid false positives. Up until now the approach worked well, and the problem this time was the docs.rs team missing the alert. Unless this starts happening consistently I'm not sure this warrants a ton of design work around automation.
We're also planning some infrastructure upgrades to better handle the increase in the number of publishes: right now it's kinda hard to scale due to some architectural decisions, but we have a workable plan to be able to scale in the coming months.