I personally dont think they'll ever have any true use. Look at 3 bosses for instance. Predator was removed long ago and replace with Karan, we lost all Pred seals we had, though he may come back as the Abyss boss. Master Mong and Mad Ray, while still in their respective rooms, were demoted as bosses, and their seals were removed as well.
Its been nearly 3 years since Trick first opened? I just dont see them doing anything marginally important with boss seals.