One of the hardest losses for Lexus and the GS is dropping the GS F. Even if they come up with a next gen IS F, the amount of dead space between a ~$65-70k IS F and a ~$120k LS F is too much. They can't do anything with a FWD ES, unless maybe the next gen TNGA FWD platform can accommodate a much higher performance AWD system with better balance and weight distribution. That's a decade away.
At this point, I think it would make more sense for Lexus to drop the RC than the GS, and reposition the GS as a four door coupe like we've all been saying. The GS is selling 2x+ RC numbers.
IS F
GS F
LS F
LC F
... is a decent lineup, but without GS F, the whole "F" concept really means very little. One "attainable" car with IS F and then two halo $120k models at the top? There's no continuity. No consistency.
Lexus' best bet is NX F and RX F, but again, I don't think TNGA has the capacity to support high performance AWD and high horsepower applications in FWD-biased cars like Audi does.