So what has happened since then? Well, the work necessary for an initial release can be split into four different sections:
Make it more obvious what is going on in a campaign

Mission briefing
When I asked beta-testers what they thought of the missions, they were not aware there were missions. This means they were unaware of the strategic side of the game completely, and had just flown around and shot at things. It wouldn't have been obvious what the other AI planes were doing, that there was a battle raging high in the skies above, and that there were people on the ground fighting for bases.
This is 100% my fault - I was going to rely on a wiki-style website to provide more information, but this wont help anyone but those already interested in the game.
So I'm adding messages & hints to coerce the player into opening menus & investigating what is happening within the game, and more messages pop up around important but off-camera events during the game.
Make the plane nicer to fly - improve the 'feel'
While most of the experience of flying in the game is fun, there were still some rough edges - especially take offs & landings. These have now be smoothed out, and look a lot more realistic.
Fix bugs

Reinforcements arrive at the front line
Complete features & content
There were some features still not present in the last beta, that I considered necessary - realistic gun damage for all types of guns / aircraft era, ability to add rivers to a map (and have the planes able to interact with the water), remove air brakes (and wheel brakes too) for planes that historically didn't have them, etc. These issues are either already fixed, or in the process of being fixed.
Probably most of the work left is creating new content - maps, scenery, and planes. I cant promise what will go into the game before the next beta, but I'm hoping all code changes will be done, and I'll just have content to do before the game is ready for release.
As always, please keep your eye on this website for updates.