+1
Totally agree. I was in exactly the same position as you.
People talk about fiat holders but we are dealing with a trading scenario and for most it was probably just a question of timing as to whether we were in coin or fiat. There is no such thing as a "fiat holder" in the context of a crypto exchange.
I disagree, when you trade BTC for fiat each coin can have only one owner at a time else there would be an imbalance. eg. for BTC/USD there must be one BTC holder and one USD holder at completion of the trade.
The IOUs created in the trading database can each only have one recipient, and must be honored as they were at the time of the last trade (or rolled back to the last backup snapshot which would be worse) You can't have two people claiming ownership of the same crypto coin or the same fiat which is what you are trying to do by disregarding the holding, timing is everything.
Converting balances based on available funds doesn't leave multiple people claiming ownership of the same coin. BTC-e didn't segregate user coin accounts (they pooled wallets). Bitfinex even socialized losses as mentioned above despite segregating user Bitcoin accounts.
The point is to create solvency on the books. It makes sense to denominate the losses in a common currency, then redistribute based on the lost amount. The tokens need to be denominated in that common currency (eg USD). They don't need functioning fiat capabilities to redeem the USD token value. They can do that in other coins at the time of each distribution. And since it will be based on current market value at each distribution, users would be fine with that. Just like Bitfinex.
The trouble, of course, is that they have to reconcile a lot of accounts. And they need to do
something with the shitcoins that are socialized. That does make this tough.