for me, the
#1 killer feature that would move bt from test/dev/play-around to production/live is supporting a high quality data feed provider, like iqfeed in US. As IB datafeed is not very accurate or reliable.
#2 is supporting some kind of persistent storage (postgres, influxdb, mysql etc) for both ohlc data and trade/backtest data.
Also it would be remiss if dont mention the #1 killer feature bt has right now which is ease of use, I was able to get an algo up and running with csv in less than 10mins of discovering the package and so far all the issues I have run into are either timezone specifc or something silly with IB :(