Check out the Liquidity pools BTS have come out with: https://docs.bitshares.build/docs/liquidity-pools/liquidity-pools-intro/
The relative ease of creating a bridge on BTS is why I am bullish to connect Hive and BTS more robustly. Both are built on Graphene and would complement each other vs compete.
Yep, the problem remains the same. If there was a BTS/HIVE LP or whatever, you need both BTS and HIVE in that LP to make it deep enough. Probably most people would want to move from BTS to something else, which means an additional step that doesn't exist in the case of a BTC-HIVE bridge or even a BNB-HIVE.
Anyway, from what I know, BTS is supported on Hive-Engine in its wrapped form, as are all or most Graphene-based coins. Having liquidity or volume is a different matter.