With the time lag reflecting that it takes a few weeks to collect and process information from individual airlines, BITRE has only issued Australian international passenger and freight aviation statistics for January 2019.
Given that the majority of international leisure bookings to southeast Asia and beyond are made at least six weeks in advance - and many much earlier - one may not be able to discern any 'backlash' from this Sharia law imposition until about the June figures.
It's complicated by how BI has also (particularly northbound) had a major timetable change ex MEL with introduction of nonstop flights BWN to LHR instead of the previous one-stop via DXB. This change meant that the previous same day both-ways Asian connections were no longer available northbound, requiring STPC (airline provided free hotel stay) in Brunei. This has made trips MEL to Asia on BI unattractive for most. One agent I know who used to book many passengers onto BI says his business with it has dropped to practically zero, as clearly it's concentrating far more on the MEL - LHR market (and typically pricing at the bottom).
A further difficulty in assessing reaction is that because BI's fares tend to be the cheapest, in theory (if better known and effectively promoted) it could fill its sole aircraft to and ex Australia each night/day because demand for 'cheap seats' is more than the capacity of one aircraft. However knowledge that this airline even operates to/from Oz must be lacking in the general community and nor do big travel agents promote it much (although latter is true for many airlines such as AC, CA, KE, MU, NH, OZ, PR to name a few - how often have you seen Flight Centre promote these?)