/p terrain would be a plot command that generates a chunk of randomly generated land. It would be level with the ground to avoid really tall and square chunks of land. You could specify a biome at the end of the command to generate specific terrain (i.e Extreme hills, Plains). This would be useful for players who need to build a naturally generated piece of land that are really bad at terraining.
I believe there already is a command for this, but it might be that owners only have permission for it... Not quite sure though.
Owners only, more specifically, Quicksteve. I would know this because I have often crashed the server with this command.
I vote no. It has the power to crash the server. (I know becuz I had leo do a "extreme hills" biome on 2 megaplots)
I don't see an issue with this if it only loads the top layer as terrain. Just no extreme hills or oceans.