Based on comments of ?KenBloom in WhateverHappenedToTesting

The goal of this idea is to come up with ways to delay riskier packages longer in unstable so that there is a higher chance of bugs being found before the package propagates to testing.

One Thought: Do not allow urgency=high or urgency=medium unless the package closes an RC bug that is already in testing. The testing propagation scripts should be augmented to figure out from the BTS which bugs are in testing and which are only in unstable. If there's no closes: #xxxx line for a bug that is in testing, then the urgency= line should be overridden by the testing scripts and treated as urgency=low.

Another Though: make it take longer for a package to propagate to testing (although this has its downsides).