We dropped exact bitcoin API compatibility as a goal because bitcoin's api is terrible. Instead we exposed the same functionality in a way that makes sense in our system, which means it can't be a "drop-in".
It would not be hard for a dev who was experience with OB and BTC clones to integrate bitUSD at this point. We have send to/from address, public accounts, multisig, and coldstorage+offline trx all coming in 0.4.25