When can we expect new content in alpha? Is there going to be anything else? Or will everything else be held until release?

As per the larian twiter there should be an update this week that releases the Dwarf origin.
There will be bug fixes and balancing done in the patch as well.

What will not be added during early access is anything further than act 1. Larian wants to keep that as a new experience for everyone.

I don't think the dwarf will be in the patch, read the latest twitter messages.

I posted that before further info was posted on twitter.
That being said it seems you are correct, and the dwarf in the tweets is not related to the patch directly but may be more of an online persona/ someone to increase the lore.

Well we don't know it will occur this week. We would like to think it will occur this week. Given that they said it would occur last week one has good reason to believe it will occur this week. No one should be surprise if it is delayed another week or 10.

Yeah, upon looking at their Facebook message and Twitter activity. It seems that Blackwood's beastiary tweets are what is confirmed for this week. (The first one is out)

The update may still be released, but nothing has been said yet.

Is Act One only Fort Joy or will there be other content?

Act One is the entire island. Presumably further arcs will take place on the mainland.

There may be some content added within the first act, in addition to balancing changes, new features or expansions of existing features (such as improvements to AI, updates to crafting, etc). No new areas will be added before release, though.

Also how many origin stories are planned for the release? I have seen people say between 6-10.

It's 6. One for each race, two for humans.

Didn't play this in a while (since I finished two playthrough already and didn't feel like the first patch added/changed enough to make a replay sufficiently interesting) so I also stopped reading updates in the last two weeks.

Which leads to the question: is there word of any new significant update expected anytime soon?

The next patch is supposedly in QA, but no ETA, because if they find a bad bug, it has to be pulled, diagnosed, fixed, and sent back.

Plus 4 racial origins for the custom characters (mentioned in one of the more recent interviews IIRC).

Since you seem up to date, is there any hint about what sort of content will include?

There will be changes to how attribute bonuses work, various fixes and tweaks to lots of stuff.