Have you incorporated the Ron-Shamir Entities into this? The paper's a little dated and it's unclear whether the balances on pg. 11 are still accurate, but it'd mean at least two additional billionaires.
If I recall correctly, the paper is from the time when bitcoin was trading at about $10. With my rake model, these entities have since shed 70% of their holdings, on average. I have included 350k DPR hidden stash and 400k mystery owners + all that I believe beyond reasonable doubt have 100k or more. The rest is statistics. The difficult part is that we don't know if for example Winklevoss have sold a part of their coins or not. They are sitting on 10,000% gains and their price projections are conservative so they may not be über bull.
The possible existence of large hidden holders is something that cannot be ruled out, still. The 400k may be 1-2M if somebody has a masterplan. At any rate it does not affect the rest of the distribution, and due to bitcoin's crashy nature, even economically I don't think these pose a threat. They are in position to do wonderful things though upon coming public
Tinfoil alternate theory I now posit (which should hold at least as much credibility as the above-referenced study): The Winklevii are Satoshi Nakamoto, but their over-trust in Zuckerberg taught them their lesson on how not to create and release virally-adopted technologies, so they played this one close to the vest, knowing in a few years they can parlay their influence within the elite to guide regulatory acceptance, as well as launch a spike in investor confidence when the stage is set. Then they will own not only the original Satoshi coins, but their own publicly known purchase amount (why so much by an elite??), and control massive amounts more with their ETF. In 2033 they will issue a royal mandate renaming the currency Winkles.
Only their benevolence will save us, but I fear a genetic purge of those below six feet in height...