Picking up spawners is the big one, which people might disagree on, but spawners are never going to be a top tier farm, they are super rare, super manual and highly unreliable to 'farm'. Picking up silver fish doesn't seem neccessary, but why not, one more item to collect and probably cool to have something besides chicken eggs to store mobs in chests.
Actually, you can already mine the dragon egg, provided you block all spaces it can teleport to.
