In the last few weeks I've been working more or less in parallel on the new major features (selective immigration, and new game modes). It's definitely not hard stuff, compared to the furniture update in Alpha20, which required redesigning big parts of the game's engine. I've had some struggles though, particularly when trying to design UI for the new features. Below is an early take on the immigration UI.  
I also changed the way the game tracks items (I started using reference counting, for all the programmers out there). This allowed a more elegant design of equipment management that fixed a few bugs and quirks. For example I'm finally able to enforce the limits on the number of specific consumables owned by a minion. I could even add a UI for that, although for now it's hard coded: 40 arrows, 6 healing items, and 6 combat consumables per minion. While I'm at equipment management, I'm planning to add a clever command that combines production scheduling and assigning equipment to minions. In the menu where you order a minion to equip existing items, there will be buttons to schedule various new equipment in the workshops, and automatically assign them to the minion when they are produced. Hopefully this will reduce some of the micro-management that players have complained about. Since Alpha20 was released 6 weeks ago, a lot of bug reports have arrived (about 15 thousands games have been played out since its release though, so there's no surprise). In particular, there's seems to be a major issue with loading textures on some older video cards that prevents many people from launching the game. Therefore I'm planning a bug fixing update soon that fixes as much as possible. There is still a lot to do in every corner, and with the holidays coming soon, I optimistically estimate the release of Alpha21 around the end of January.