Well that's the point - if you take a short/long position in BTC, then you must afford to pay it out even in fluctuations - if you can't, pay someone to hedge/'insure' it; if you don't - declare bankruptcy and pay up whatever you have.

The whole point is that 'comparatively small' players shouldn't be allowed to take up insane amounts of volatility; if you accept consumer's money then it would be reasonable to require to put that $25mm as a bond to pay out your debts, and put a ceiling on how much deal volume you're allowed to hold if you've got only tiny amounts such as $25mm.