This is a little idea I had that would make the task of exploring the stronghold a lot more daunting than it usually is, because as of now, it's a complete walk in the park, and silverfish are a near non-existent threat, with only the occasional creeper of other monster getting your path while exploring the structure.
Silverfish would sometimes spawn outside of their blocks, and would have slightly tweaked AI so they wouldn't immediately jump into a block if they spawn this way. Now, when exploring the stronghold, you still have to be careful not to trigger a silverfish cascade, which is usually the least of your worries when trying to find the stronghold portal. Silverfish in general should also have a *much* higher social spawning rate (a feature that allows certain mobs like zombies to spawn other zombies in when you hurt them) than any other mob (probably around 33% to spawn another silverfish when hitting it). To balance the constant spawning of silverfish, they wouldn't spawn unless there is a sufficient number of infested blocks nearby.
This feature would probably be reserved for harder difficulties, but I think it would be good overall just to make silverfish relevant again.