They could issue bitBTC instead of open.btc and bridge.btc... then the trading and long-term holding of assets would be risk-free for users. The only time when they fund would be in other's hands would be when depositing/withdrawing real BTC. After bitBTC proves to work, others could follow.
Gateways would have to use their money at the beginning as a collateral to create bitBTC. A small fee could be introduced on trading bitBTC which would be used for buying BTS at the open market which would indirectly lower gateway's risk.
This is more in line with the potential response. The issue simply stated is that the overall network would benefit from a concentration of trading volume to make the DEX more attractive to other traders. A committee run escrow account could be a solution but either way it would be helpful to have the gateways themselves on board. This is where the Federated nature of "Federated Gateways" comes into play.
Of course the risk with bitBTC in that way is that it is shorted so it can black swan. which would cause a pretty big scandal if people had deposited.
I guess you would also lose the direct relation with how much gateway.asset is deposited and how much they are holding.
bitBTC could be utilized in this scenario if the community directed some of the shared treasury to support the bitBTC market.