I think the biggest problem with Toyota/Lexus/Crown/Century is there's been too much consolidation in the platforms and drivetrains. When Lexus was in it's peak, the 1990s and 2000s, they had drivetrains that were exclusive to the brand. The SC, GS, and LS all had inline-6s with V8s being an option. With the exception of the I6 in the Supra, they didn't share a drivetrain. Even the original IS300 had the inline-6. SC and IS were available with manual transmissions too! Only the ES shared a drivetrain with the Camry. Now the Century shares a platform with a RAV4. It's embarrassing.
Lexus/Century/Crown would really benefit from a new rear-drive platform, and more engine options. They need a new turbo inline-6 (which could be given a longer stroke for future Toyota BOF applications) and a TT V8. That TT V8 could then be exclusive to a new SC, LS (SUV?), LX, Century, and maybe some high performance products (GR Tundra, GR LC300, GR Crown Sedan, IS-F).
Interior design needs to be stepped up too.