I'm really having much fun with Vitalize the Land - what about enhancig the terraforming options?
Here are some ideas:
- workers can turn grass into plains
- settlers (or a special terraformer unit, maybe dwarves) can both flatten and create hills; they are consumed by this action
- additionally, adjacent peaks will be turned to hills, and coast to flat land
- Meshabber of Dis should leave a trail of destruction, automatically turning the tile he's occupying into desert and remove every resource, feature and improvement (hey, this is Armageddon after all

)
- add another, similar demon which leaves a trail of ice instead (or even ocean?!)
- Druids can create rivers and floodplains. Maybe force the Terraintype to desert then (and maybe don't change floodplains with Vitalize the Land/Genesis, so that food yield is limited to 3, not to 4 or 5)
- Octupus Overlord state religion allows the construction of a powerful sea demon that can turn adjacent land tiles into ocean