the main problem of the 10-12+ hours routes is that you need more than 1 frame. JFK allows for 1 aircraft to be used, while the advantage of LAX and SIN is that SIN arrives in the morning allowing for a LAX-turnaround arriving next day afternoon connection to the evening SIN-departure.
combining only LAX and JFK is a bit tricky because there is not much buffer for delays or small technical issues left which would lead to inconsistent deployment of the new La Premiere which the high paying customers will not appreciate
Just as a side note and maybe more general comment on LP / new LP / demand: I think the FT community overestimates the importance to -- maybe even awareness of -- the "normal" LP passenger that the flight will have the new LP cabin or not. The "normal" LP crowd that flies between CDG and LAX or SIN will fly it regardless whether the cabin is new or old. On the JFK route, the typical LP passengers are driven by schedule and availability (sometimes flights are P0 F0, sometimes they are P4 F1, and anywhere in between). In fact, on my last two flights in new LP, the cabin was 2/4 while other JFK flights were sold out in LP. People are not clamoring for the new LP.