I think we can categorise the tasks into two types: overall (the countries, the map, the tech trees, the models, the crucial events, graphics) and per-country.
Overall tasks
Countries: All done, although there's still some tweaking to be done (national and claimed provinces, whether Finland should actually exist in 1914, etc)
Map: Done. However, there was talk about altering population and IC levels, and victory point provinces, and I don't know if anything's actually been done on this.
Tech trees: About 60% done, I think - Johan would have the best information as I believe he was looking after this area. However, I don't think we have any flavour text written up, just the tech names.
Models: I know various things have been posted on this, even back in the original megathread (eg DrBolo's work) but I don't know if anything's been finalised or coded.
Crucial events: We have the July Crisis, the US entry sequence, and about half the Russian Revolution in place. I'd say we also need Italian war entry as a minimum, and perhaps the peace treaty events. Everything else would be "flavour".
Graphics: We've done most of the title and loading screens, alliance graphics, victory point screens, etc.
Per-country requirements
I think this would be simplest shown as a table, with country names down the side and categories along the top. For each country, we need:
Flag: - I understand we have all of these (except perhaps for Makhnovschina (a plain black flag?) and Ulster (white, red cross, red hand)). However, I don't know if they've been collected into one place yet.
Description: There are about a dozen of these completed, I believe.
AI-file: I think Johan did a couple of these, but most are still not done.
Ministers: I believe we have most of these now, at least for the major powers.
Leaders:I'm not sure how far advanced we are with these - a lot was posted early on.
Orders of Battle: Land, Sea and Air. I think we have all the information, but I don't know if the naval and air OOBs have actually been coded. (I posted some info on air OOBs in 1914 a while ago, in the relevant thread). However, there are some anomalies to sort out, like Britain getting its full Kitchener New Army in January 1914.
Supplies, convoys and resource pools: These still need to be set up for each country