Decred, thanks for the detailed response to my questions. The attached spreadsheet is absolutely clear and I encourage anyone with concerns about ths distribution of coins to look at it.
Starting with 50% of the coins at launch and 4% of the total does not entitle c0+devs to 15% of all minted coins. The reason is that 60% of the subsidy goes to PoW miners, which c0/devs have no overlap with. The plan is to have a few GPUs mining Decred after launch, but 60% of all the coins end up with PoW miners. When these coins are held by PoW miners, or whoever they sell it to, they can be used to mine PoS themselves. If coins are voted in proportion ('in proportion' explained below) to the amount held, the 4% premine turns into 7.32% of the total at the end of year 5, which is assuming none of the premine coins are spent. This means that c0/devs have 4% turning into 7.32% in 5 years, not 4% turning into 19%.
Let's make sure we're comparing apples to apples here. The 19% figure I gave was how much of newly minted coins the c0+devs would be entitled to if they had been staking since day 1, and includes the 10% dev subsidy as I was lumping together the dev org, devs, and c0. Perhaps it wasn't fair of me to lump the dev org together with the c0+devs as they may not be the same parties, but my point was that 3 organisations will obtain a % of coins that are not available to the general public (and my ~19% figure is correct).
If we separate them though, what your spreadsheet shows is that at the end of year 1 the c0+devs hold 24.42% of all coins to date, which entitles 7.326% of all coins being minted at that time (24.42% of the 30% PoS reward).
Your spreadsheet also shows that at the end of year 1 the dev org will hold ~341k coins, or 7.376% of all coins to date, which entitles them to 2.2143% of all coins being minted at that time (7.376% of the 30% PoW reward).
So these two/three parties between them will hold a total of ~31.8% of all coins to date after year 1, entitling them to ~9.5% of all new coins via PoS (31.8% of 30%), plus the dev org would continue to recieve their 10%. So I stand by my point that after 1 year, 19.5% of newly minted coins would be going to the devs/c0/dev org, i.e. not the general public.
But all of this is conjecture and assumes that none of the dev+c0+ dev org would have sold any coins, which is unlikely be the case.
I think it is also important to stress that I'm only demonstrating this for transparency. I have discussed with decred the rationale behind staking the premine coins and I agree that it is absolutely necessary for several reasons, not least that the PoS network needs to be secured until there is a significant enough distribution of coins
So the TLDR is that, yes the premine coins held by c0/devs will be staked, but it is both necessary and fair.In the event that there is a low participation rate in PoS mining, the plan is to throttle c0/devs' PoS mining so that it does not hoover up all the coins. The goal with PoS is not to hoard the coins, but to create a strong incentive structure for users to participate in securing the network with their voting. c0/devs will not mine more PoS than projected in the "everyone mines" scenario, as it would go against the spirit of the project.
This is the key to answering my concern, it essentially means that the c0/devs will not stake more than 50% of the coins being staked by everyone else (at least once the network is secure and a good distribution of coins is being staked by other people). It's going to be a challenge to achieve this in practice!
Anyway thanks again to the decred team for being transparent.