I get redstone, because of the fact that some servers don't want it, but why not mob AI. That's less of a headache than redstone, as you can simply disable mobs, or just their AI. But I guess the same argument could be made vice versa.
If it can be disabled, it should be a plugin so that the server doesn't have to load the unnecessary code. We are planning to move all optional features out of the core into plugins, e.g. RCON