Correct me if I'm wrong; there is at most, 4-5 QF departing flights worth (1500-2000 total pax) at Singapore at any one time. Even if 100 of these passengers were Emerald, that would be a high number, no?
BA F/Emerald pax will no doubt be making their way over. As will EK Plat. And MH Emeralds making the trip from T2..... and Jetstar... and the savvy CX pax who do the loop-de-loop via T1 instead of T4.
Methinks maybe the new lounge is about making cash from other airline pax (via intra-airline lounge fee agreements), rather than it strictly about overcrowding of existing lounges. Sneaky sneaky QF! (I love it!)