Assuming that the Paradox team has subject matter experts for each is probably a bit unrealistic. I could come up with a focus tree for Australia pretty quickly as well (although it wouldn't be as good as the one in TfV).
Anyways, to call your bluff, how about that plan for China in 10 mins? All you need to have is something on a piece of paper, take a photo/scan and post it up. It needs text for each focus tree description, the bonuses and of course the flow.
The reason I keep 'calling your bluff' is because something humans (me included, I'm a human too

) consistently underestimate the difference between an idea and how much time/effort it actually takes to make something happen. This happens even to people that are experienced and established in a field. I don't mean any offense by suggesting you're being affected by this (I've just said it's a species-wide thing, so at worst I'm insulting our species, assuming you're human as well

- but I don't think I am, I think all species have strengths and weaknesses, and accurately forecasting the amount of time it takes to do something isn't most humans do well unless they've had a lot of practice doing it).
.
Ill do this because I'm tired of people making excuses for the ridiculous price gouging of TFV.
Here's my 5 minute China Bullet List-
industry/infastructure
Move Industry To Interior (Requires War With Japan, 30 day focus), similar to Soviets, no net industry gain, moves industry from coastal areas to interior
Fortify the Ports: Add coastal defenses to any port with level >3
you could even do something tricky and make fortify the ports mutually exclusive with a fortify the Japanese border, which adds level 3ish land forts on the border provinces with Japan, but prevents you from fortifying the coastal provinces.
One or two civilian factory foci (3 factories if 1, 4 factories if 2)
Two military factory foci (5 or 6 factories net)
infrastructure foci- 1 or 2 infrastructure to a few states
Naval focus tree- 6 dockyards net but gated to require China to control port arthur, prevents early fleet build up.
Political tree dealing with Chinese Civil War- this will be a bit tricky to work with given its all handled by event now and the time frames involved given the early Japanese invasion. If the focus tree deals with this, it will either have to be quick foci (30 day) that gate all others, so that you have to decide what to do prior to Japanese invasion, or will only be foci that deal with the aftermath of a Chinese victory over Japan. This is the portion of the focus tree that I need to think about for more than 5 seconds.
International Assistance-
American Lend Lease (infantry equipment, could be net, could be bonus production, etc)
American Volunteers (air support mainly, fighters, fighter doctrines, airfields)
Soviet Volunteers (Not sure how large soviet contribution was, need some research)
Burma Road- infrastructure boosts on indian frontier, infantry equipment
German Cooperation (Currently a national modifier at the start, land doctrine research boost)
Ahistorical- Additional German assistance (for a germany that chooses not to withdraw advisors)- land doctrine bonuses, armor research, close air support research. You could even do something like adding another focus or two to the german tree if they choose to support China over Japan, where China gets a fascism boost and potentially an axis invitation if they so choose.
The big gameplay addition- I want a revamped partisan system that significantly effects supply throughput, to the point of lowering it to almost zero. In addition, offensives/taking provinces should take large amounts of supply to enact. I think the bulk of your supply throughput should be for just keeping your armies supplied while not moving, and that major offensives should require a supply build up prior to launching them to be effective.
The land doctrine planning bonuses could be related to this as well and reduce supply usage. The grand battle plan doctrine will get bonuses to reduced supply consumption while using planned offensives (no manual control!) in addition to the planning attack bonuses, while the mobile tree will get supply usage reductions on unplanned offensives to reflect the greater freedom for improvisation. I want it so that your troops won't be able to be resupplied on unplanned offensives unless you're on the mobile path, and you can only attack deep into China if you have a full planning bonus offensive going. Basically, partisans will severely impact supply throughput to the point where if suppression divisions aren't employed, troops will start to starve.
In the Chinese theater, what stopped the Japanese weren't the Chinese main armies, in fact their combat losses against China were quite low. It was difficulties in supplying their forces due to the poor infrastructure and partisan activities that halted their offensives. I want China to have a boost (+50%?) to partisan strength, with the goal of starving the Japanese armies as their supply lines get extended. The main effect of partisans should be supply, not factory sabotage. This will obviously impact other theaters, in particular the Russian front and maybe Poland can get a nice partisan boost as well.
This will allow Japan to take the coasts, and launch large preplanned operations (planning bonus), but as they move inland their supply lines will become longer. Here's where the partisans taking out the Japanese supply routes come into effect. With the extremely poor supply throughput their attacks will become weaker the deeper they get into China, with each province they take stretching their already extended supply line. The goal here is to make the war stalemate, where Japan can't advance effectively anymore without heavily investing in securing supply routes for their main combat forces. Of course, the main issue with this is the AI needs major revamping and ability to actually deal with unrest effectively, otherwise it will cripple the Japanese and German AI.
China could have several foci related to the partisans. There could also be foci related to peace with Japan if China controls Manchuria, perhaps an extended chinese civil war tree could come after this with choices on striking a deal with the communists, war, appealing to the US, etc.
There, there's a rough chinese focus tree story board AND the major overhaul/addition for an expansion that might fix the Sino-Japanese war AND make the eastern front last until 1945 in 5 minutes. You're welcome Paradox.
edit:
In that case, I'm even more surprised by your concern over TfV's price. If the overall package is $15, and we assume $5 is the sprites (the Rights of Man sprite packs cost $5.99), and $5 is everything else in the DLC (not unreasonable), then you get a price of $1 for each focus tree. Now, this may not be how it was budgeted internally, but this is far from an unreasonable assessment of the cost of each component of the DLC.
For this, note I said MAX. Ideally it would be like $0.50. Which is still significant return on investment, if it takes one employee 3-4 days to make a well though out focus tree and they sell 100,000 copies for $0.50, I'd say that's a great return for Paradox. And as I said, I want nothing to do with the sprites and portraits. Those are purely cosmetic, I shouldn't be paying for something that adds nothing to the gameplay unless I want to.