And you could make a challenge mode with something like this make a self contained food/lumber system before the goo eats it all.
That actually sounds like a really cool idea. But I should probably remove the goo bug, and replace it with an actual species that is so efficient that it destroys all other life.
Maybe some kind of fungus infestation/lotus swarm. The animal version would be xenomorphs :)
An interesting thing in the challenge could be how to contain it. Maybe barriers can be built to prevent it's spread for example.