I've just booked a Star-Alliance J award using SQ Krisflyer points on Turkish. While there was better availability Europe-MEL compared to SQ, nine months ahead, there are some things to note about this:
1. There were only one or two days per week with award J seats IST-MEL
2. J seats from European ports to IST were fairly easy to find as long as you aren't using an SQ-served port. Basically, anywhere SQ flies out of, you won't usually find availability on TK using Krisflyer. So, no seats I could find out of CDG, FRA, MUC, AMS, BCN, VIE, MXP, etc, but readily out of secondary/other cities all over the place. (I searched western European ports, excluding Scandinavia.) A potentially useful aspect of this is that if you aren't quite sure where you would end a trip you're planning, but know the general region, you could choose among a few fairly close options to work out the best compromise solution (e.g. for western/southern Germany there's at least Stuttgart, Nuremberg, Cologne, Düsseldorf, and more heading northwards or eastwards; for southern France you could keep Marseilles, Nice, Lyon, Toulouse, Geneva, Basel, Bordeaux in your sights.)
3. Some of the flight times don't work for the onward long-haul connection, especially for the westernmost ports, unfortunately, resulting in an overnight in Istanbul.
4. The short-haul to Istanbul adds about 30K miles (total 133K SQ miles) and $, which isn't great value IMHO (and these flights are mostly "EuroBusiness"-style or only a bit better), but the convenience is significant, given how hard it is to get "feeder" flights on the same ticket nowadays. The total surcharges Europe-Melbourne will unfortunately be around €350-400 (A$600-ish). Flying out of Switzerland comes in a little cheaper, around $530, at current awful exchange rates.
5. Seat selection only works via the TK app, and will throw errors of various sorts in the process (but the seat selection nonetheless works, at least for me). There are some reports on FT of it not working, but it might partly be people's reactions to the error messages.