I am not sure there are enough trustworthy people whom it would not be insane to trust with this much money, and to not collude to try to steal the money.
BTC500 to be held by one single person? Definitely not. Not anyone. I think those funds are at risk.
7 people for a 4-of-7 multisig address so 4 signatures are required? Absolutely yes. Much less trust is required in that case.
First of all, this is ultimately theymos' money, legally speaking, so the decision starts and ends with him.
In order for it to be a good idea to allow someone to hold 500
BTC of your money, you need to be confident they can be trusted holding said money. This is very straightforward as all you need to ask yourself if the person can be trusted with said amount of money. OgN has shown himself to be able to be trusted with the money -- he has not touched the money, even as its value exceeded $10 million, this is true even if you need to ask probing questions when relying on information provided by him.
If someone were to be a keyholder of a 4-of-7 address, they need to be similarly trusted. They perhaps to not need to have sufficient "trust" -- that is confidence they will keep their promises when amounts involved are in the millions, not having a bunch of ratings for $200 transactions and for having "good judgment" -- to hold 500
BTC, but need enough trust to hold very substantial amounts of others' money.
If you were to rely on the fact that two "people" are truly separate people, you will have difficulty verifying this information. First you need to verify they are two distinct people, but this is difficult because locations can easily be faked. Next you need to evaluate if the various keyholders have existing business or personal relationships that might conflict with the assumption the keyholders will not collude to steal the money. Two people that run a business venture together are going to be similar to being one person as they are likely to be loyal to eachother, and their financial success not only depends on the others' reputation, but also their financial situations are likely to be similar and will depend on how successful their venture is. The same is true if two people later form a venture after becoming a stakeholder. if two people have frequently traded with eachother, or are otherwise friendly, they may not disclose an (unsuccessful) attempt to collude to steal funds as a "joke" or would not otherwise report such an attempt.
If there's going to be a multisig treasurer system, wouldn't it make sense to only pay the treasurers for their services after the funds have been paid back?
Is there an overview of past returns from treasurers? I know one was lost, but I don't know how the others did. I'm curious if it's been worth having treasurers over just Admin keeping the funds.
The service is to hold the money, potentially for years (as has been the case), and to maintain the private keys holding the coins. Coinbase
charges 0.5% per year to hold coins similarly to how the treasurers are holding funds. Gemini
charges 0.4%/year. OgN's payment is probably a bit on the high side, but both he and theymos are free to negotiate a price they wish.