We now know a few more details.
It’s currently going by the name 0x10c, and will feature a persistent online world and multiplayer.
According to Notch, it’s an “ambitious” space game that will combine battles, an economy, engineering, planet landings and multiplayer. Like Minecraft, Notch is planning to release early versions of the game in a bid for players to contribute ideas and thoughts that will possibly affect the final product.
Notch also said that a monthly fee will be likely for these players wanting to join the “Multiverse”, as that will feature a persistent world. However, single player will not require any extra payment.