thus even in a stable exchange. your supply buffer would not be the same. and because there is lack of supply. people can abuse that. by arbitraging. and only using your exchange as a temporary 'flip' rather than a permanent store
This got me thinking, so I'd like to clarify this "flipping".
I think you are stating that traders could use the buffer against itself to make a profit on trades.
That is they buy at the buffers lowest bid, and sell at its highest ask, but the buffer doesn't post trades that other traders can see, it only reacts to trades that others posted. The rules that define how much it will buy/sell are strictly enforced but easy to calculate what the buffer will buy and sell at in any given moment.
Also bear in mind that the conversion of EMU->BTC/USD/GBP or anything else is frictionless and costless to the buffer, its a zero sum game. If it didn't receive any new supply, and started with 1M units of the base asset, it could convert all of the USD, GBP, BTC token assets it made back to the base asset and it would end up back at 1M (this is due to the FIFO conversion queue).
So lets say that a trader A thinks he can profit, the buffer only buys if the ask is below current price-max delta, and only sells if the bid is above current price+max delta
With that in mind, how could he profit, I don't see any immediate means to do it?