Restricting total posts (rather than per contributor) would make posting a rare/scarce resource, making people want it even more. Picking a system to pick who does and who doesn't get to post opens a huge can of worms.

Restricting the number of promotions sends a message that promotion isn't based solely on quality, popularity, and importance, it's also intentionally biased by accident of timing. This could cheapen it.

I'd write a post on how writing a post at busy times may be irrational, all else equal, because (for example):

• Less people will read, comment and vote on a post that's lost in the crowd.

• It's less likely to capture the attention of busy promoters, even if they're trying to stick to promoting based on good reasons.

• If you wait a bit rather than posting so early you'll get a better idea of what kind of post is better understood, more useful, and considered higher quality.