All DLC shows as purchasable, although I bought the Supporter Edition (middle option at about US$70) during Beta phase. I have never received any emails, but just an available download on steam.
EDIT: After reviewing my old emails and bank statements from July 2013, it appears that I ended up buying the game on Steam. I can only imagine after going through all the research to learn about the different beta versions that I must have gotten frustrated with BI store issues at the time, and ended up getting it from Steam. It's a moot point anyway, because I've also just discovered that the version I had intended to buy from BI Store was the middle, Digital Deluxe Edition, which didn't include free future DLC. Sigh... Please disregard this post.