Me and my gf got around 500 hours of content out of the current build.
Though we do spend a lot of time messing around with building bases and gathering stuff, if that's not your thing, your hours may be cut in half at the very least.

The game is amazing as it is, but the updates are slow because they are a small studio who just happened to stumble on massive success. So a lot of the community treats them like AAA devs and expect large rapid updates.

Though I can tell you that the developers care about this game and the community a lot and will 100% see it through to final release.

I wouldn't expect further major content after final release though as this is not sold as a service, but rather a game.