You'll get a Steam key as soon as you buy it.
Grab it here:
https://www.humblebundle.com/store/the-real-texas-dusty-skies-edition
You can also buy them separately there for a discount, in case you just need the DLC it's 10% off:
https://www.humblebundle.com/store/the-real-texas-cellpop-goes-out-at-night
In other news, I absolutely have not forgotten about the 1.7 update. I worked a bit on it yesterday. This will be a bugfix update that also improves compatibility on Linux, and in particular fixes some achievements.
It's been on the back-burner for a few weeks now as I've been working intensely on Paradise Never. But I'd like to wrap 1.7 up soon so I don't have it sitting there in the back of my mind, taunting me :) Stay tuned!
As always, thanks for your support!