Secret Seeds

[funnyduck99]

In terraria there are secret seeds that really change how the game is played. It would be cool if that came to Factorio. Maybe some start you off on different planets or even in space. One could make every type of enemy spawn on all planets. Maybe it changes the tech tree around or completely change world generation.

[Prezombie]

While it's a neat idea, and a great way to squeeze easter eggs into a game, it does have several downsides that make this unlikely.
If you let the seed be a cheat code entry, it makes having a seeded run with a specific code difficult.
It's a very opaque feature that you would need to already know about to use, and the devs have tried to keep that as minimal as possible for such a complex game.

We already have mutators and a very robust scripting and worldgen system for making more complicated changes with mods, and is far more open than a random silly idea. There's already nearly a dozen other scenarios and alternate worldgen defaults to choose from in the base game alone!

[Kyralessa]

In terraria there are secret seeds that really change how the game is played. It would be cool if that came to Factorio. Maybe some start you off on different planets or even in space. One could make every type of enemy spawn on all planets. Maybe it changes the tech tree around or completely change world generation.

A lot of this can be (or already is) done with mods.

Start on any planet: https://mods.factorio.com/mod/any-planet-start
Start in space: https://mods.factorio.com/mod/SpacePlatformDesigner
Start on Fulgora: https://mods.factorio.com/mod/fulgora-start
Start on Vulcanus: https://mods.factorio.com/mod/better_vulcanus_start
Start on Gleba: https://mods.factorio.com/mod/better_gleba_start
Start on Gleba and suffer, apparently : https://mods.factorio.com/mod/gleba-nightmare
Pentapods on Nauvis: https://mods.factorio.com/mod/gleba-on-nauvis
Also pentapods on Nauvis: https://mods.factorio.com/mod/nauvis-stomper-spawners
Enemies on Fulgora: https://mods.factorio.com/mod/Electric_flying_enemies
Behemoth demolishers and behemoth pentapods: https://mods.factorio.com/mod/behemoth-enemies
etc.

There are currently 7181 mods on the portal that apply to Space Age, so you're likely to find some interesting ideas.