As developers said it is not just SnowRunner expansion, you'll get better physics, graphics, and different mechanics including something like managing convoys, building roads, and transporting raw materials, which are not just abstract boxes or containers, but materials like sand, which can change the terrain if you unload it on the ground.
As we understand after some natural disasters some places, and settlements were destroyed, so you as a player have to rebuild everything. On the release, the game will have 8 different maps and 3 unique biomes, but because the game is basically a sandbox, you will choose what to do, and in which order.
The good news is that the game will support multiplayer and crossplay on the release, so no matter what platform you and your friends are using for play, you will be able to collaborate.
You should be able to try open beta only on Steam which should start on February 24 till March 3, and you don't need to have a preorder to try it out.