Disk brakes, as on front-and-rear with KLR650s, resist fading. Drum brakes (as on rear wheels of some motorcycles in current production)? Another matter.
Regardless, I think brake line elasticity is a negligible factor in brake fade.
Steel-braided brake lines exist for both front and rear brakes. Since the steel braiding reduces hose expansion under pressure, the caliper pistons are more responsive to the brake lever with steel-braided lines. Since most braking effort comes from the front brake, a braided line for the front brake is my priority.
DISCLAIMER and FULL DISCLOSURE: My perceptions/opinions only, corrections and clarifications welcomed; have 320-mm rotor and braided line front, rear stock, on my Generation 1 KLR650.