Minecart with Monster Spawner

A Minecart with Spawner (may also be called a Spawner Minecart) may probably spawn mobs as it goes along its respective rail. A possibility is that it will spawn mobs when it hits a Detector Rail, Activator Rail or Powered Rail, or simply spawn mobs constantly like a normal Spawner.

This also gives the intention that they might add Monster Spawners to survival mode, as being craftable.