I highly doubt the transit concept will happen in SIN. Imagine explaining to a SIN-SYD F pax they're unable to use the F lounge, because it is reserved for those going to/from Europe only, and they'd need to go to the J lounge instead.
I'd guess the economics of this lounge only work because Qantas will collect OWE entry fees from other oneworld carriers operating out of SIN. Restricting it to a transit lounge would limit revenue pax to the ~100 QF F pax going through SIN each day, which would not make financial sense. The fact they've got 240 seats in the plan is a strong indication it won't be a transit-only lounge.