I wonder what all High Moon is doing/has done.
Are they planning to bring in more folks for content (Certain Affinity comes to mind, with Doom around the corner)?

I'd bet good money that High Moon is working on DLC/Expansion content for Des2ny, and has been for quite some time. I bet we'll see a similar formula over the next few years: Bungie focuses on sequels and possibly TTK-sized major expansions, as well as continuing the live team, while High Moon and other studios handle smaller expansions/DLC.

How many of those might be from the freely available demo version of the game?

No idea, could even be possible they have a way to exclude those users, someone would have to ask Bungie or Activision to be sure.

https://www.reddit.com/r/DestinyTheGame/comments/4i1zlv/activision_working_with_bungie_to_deliver_more/

I'm interested in the '30 million registered players' stat. There is no possible way that Destiny has sold 30 million copies.

If I have three characters, does that mean there's three registered players?

I wonder what all High Moon is doing/has done.
Are they planning to bring in more folks for content (Certain Affinity comes to mind, with Doom around the corner)?

From Engadget article when they first used the term:

"Update: We've received a response, and Activision says that the "registered users" refers to unique PlayStation Network / Xbox Live accounts, while multiple characters per account are not factored in. That's still potentially less than an exact 1:1 sales number, but reflects an impressive amount of sales since launch. Our only questions left? Why not be more specific from the beginning -- and when is the gunsmith going to be selling rare fusion rifles?"

So that would also include people who bought it used, or if you switch PSN accounts etc.

I'd guess sales are 1/2 to 2/3 of that.

I'm interested in the '30 million registered players' stat. There is no possible way that Destiny has sold 30 million copies.

If I have three characters, does that mean there's three registered players?