The Last Dogma is now available on Steam for purchase. It got a massive 1.3 update and features a SteamOS (Linux) version, which is a Steam exclusive and has a couple of exclusive voiced lines.
DRM-Free releases (Itch.io and IndieGameStand) have been updated to 1.3 as well.
"Cross-buy" option is there - wherever you buy the game, you always get a key.
Itch.io buyers get it in a few hours, IGS buyers get it from the IGS store (please note that keys for IGS will be deployed only in a few days after release, not instantly).
If you completed the game, you can now read Story Explanation / Developer Commentary.