I play with hundreds of mods, and I'm excited about this expansion.

Mods have performance and compatibility issues, and they don't always get bug fixes or updates very often. It'll be nice to have an expansion to the base game that's officially supported and which all other mods will have to be compatible with instead of the other way around.

Apart from the space part, which is arguably already present in the Space Exploration mod (a mod made by a developer who got hired by Wube to work on the official game, if I'm not mistaken), this new expansion promises:

"the ability to control train systems better, better blueprint building, better flying robot behaviour and many more."

That sounds great to me.