However, staking tokens in a relay has a financial cost and also involves risk (those staked tokens could be stolen). For a fair comparison these costs and risks should be quantified and taken in consideration against the risks and costs of a traditional order book. In this sense is important to note that a non custodial exchange does not need to hold the collateral for limit orders centralized in a single account / smart contract.
Regarding the purchase of relay tokens, what is the incentive or reward of holding a relay token apart from supporting that token?
One other thing I´ve always wondered is why the Bancor protocol does not accept limit orders that could be placed in a dark pool (ie similar to Republic Protocol), which would give the users the ability to send orders at their desired price without having to constantly monitor the platform to reach their desired price to submit they order, and the same time it would improve the base liquidity depth of the relay/smart token. Is this a planned development within the Bancor protocol? Is it maybe planned on a second layer? Or is it maybe planned to just let other projects to build this functionality on top of Bancor?
As a finale note, except for BNT and maybe some other, most tokens listed on Bancor Network are charging a spread (the bid price is lower than the ask price).