it doesn't cost anything to keep coins offline.
I'm sorry but this is nonsense.
Let's forget about multisig for a second. Storing coins
always has a risk of loss and theft. For all offline computer and paper wallets suggestions, physical burglaries exist too and it won't be long until we have Bitcoin-minded burglars. If the offline wallet is further protected with a password, this password is either memorized and can be forgotten (or
forced out), or it's written down and can again be stolen. There can also be a sophisticated virus, or simply human error, in the generation process.
(Myself I'm worried that the iso I would download to install Ubuntu on a fresh computer would be corrupted and actually install a compromised OS that intercepts Armory and instead of generating random keys generates keys known to the attacker. I have no idea if that's actually possible, but merely my subjective uncertainty about this possibility means I am taking a risk by holding coins. And those are just the risks I thought of - what about all the risks I didn't?)
The trustee would still be liable for the coins even if they're lost. This means he could easily find himself with a $5K debt he may not be in a good position to repay (and even if he can do it, he still loses $5K). It's very reasonable to require a risk premium for this insurance. Of course, it's also reasonable to take it free of charge as a contribution to the forum.
i don't think you need to settle for any less than 100% public reserve, with no fees.
This absolutely no reason to take the risk with anything less.
Why do you think keeping the money with trustees is risky, and keeping it with theymos is not? Utmost respect to theymos, but he could embezzle or lose the funds too and I'm sure there are other people just as reliable.
Let's assume 1%/year chance of a problem. If theymos holds everything there is 1%/year risk of losing all of the forum's money. If it's split with another trusted person, there's 2%/year risk of losing half the money and virtually no risk of losing everything. That's much better because the forum will always have enough funds to do the really important things. It's still better even if some fee has to be paid. In fact the difference is even more pronounced, since the more money concentrated at one place, the greater the incentive to embezzle and the attractiveness for attackers.
Thankfully, multisig solves most of that and allows a solution with minimal risk for everyone.