It's not the same as a promissory note from a bank because no one is actually making a deposit to a bank. This not a bank! It is a contract between two parties that one party will take on all the risk/reward while the other party maintains price stability. Maybe I don't understand how this works within the blockchain, but it sounds like you're abstracting things so they appear analogous to a bank.
Also dividends are simply a ploy for getting people to invest in you're stock. You reward long term holders of your stock by reinvesting in youre company with whatever profits you make. Stockholders profit from increases in stock prices more than dividends if you reinvest profits appropriately. Look at Berkshire Hathaway. In the case of this DAC you raise transaction fees for the purpose of providing dividends, when you could reduce the transaction fee, provide further liquidity to the markets and consequently bolster the utility of the network.
Given two otherwise identical exchange networks, which is more viable the one with higher fees or lower fees?