Wow This is cool. Good decision.
One more thing that will deepen the liquidity will be using a specific token like BEE or HIVE for every pair and drive swaps from one to other token using those pairs.
For now we have 3-4 pools of BTC with different tokens which divide the Liquidity into 4 pools. Instead we can have a single BTC:XX and SPS:XX pools and if someone wants to buy BTC from SPS, it will go from SPS:XX:BTC and vice versa. This will not only help in deepen the liquidity but would provide more trading volume means more revenue means more liquidity and black hole continues. And that XX token will have value based on tokens locked in liquidity. That XX can be BEE or any other token chosen by Engine team. and in order to incentive pool security, you can have miners stake/lock more tokens than whatever in the pool are. This is what is done by THORCHAIN https://app.thorswap.finance/ and looks like a great model. I hope we can implement some of it's parts on Engine.