The coding is not the issue. It is the semantics of the codes needs to be rich enough to represent the concepts required to identify and execute setups and orders. I.e. there is a huge middle ground between placing trades and the API. How one builds up they own libraries atop the API is where the skill comes in.
OTH, I would be interested in a 99% accurate, FULL tick by tick, backtest engine. It would have to be super high performance to deal with recreating real-time behavior. Right now, everything is truncated either in the data and or the playback. (Very difficult to roll your own, imo)