Pioneer had had a pretty rough time in development. It was originally a non-violent space exploration type game, and that is definitely fitting the leaked trailer you get while playing Watch_Dogs 2. At that point the game was already in rough shape with a good chance of never actually seeing the light of day.
Now we know what those tweets were about when they were saying “RIP Pioneer.” The game that Pioneer originally was is now dead. It is getting rebooted into a alien multiplayer shooter. It will also be using Rainbow Six’s game engine called Anvil.
Personally I think the original idea was more compelling, but perhaps no Mans Sky’s issues were something that contributed to the change.
You can find out the full story on Kotaku’s site here. Absolutely worth while reading.