To be honest, for me there is not much difference that payments for the bounty will be paid in the ETH or token of the project, because i watched when the bounty is paid in tokens, it is even beneficial for the bounty members, because the tokens can increase in price 2-5 times than the price of the tokens during the ICO.
A partial payment in ETH can reduce the number of scams related to the bounty campaigns. Nowadays a lot of bounty campaigns are not paying their participants any rewards. This needs to be prevented.