Unless that crossover into viability is preempted by some other technology. Look at oil. Everyone was screaming about the peek in supply capacity (peek oil) but that inflection point may have been preempted by a reduction in demand (fracking, electric cars, solar etc). The viability of mining the seafloor could similarly be preempted by new tech.

Oceanfloor work has already seen one such preemption: manned operations. Back in the 60s-90s everyone was talking about sending people down, but that was preempted by improvements in robotics, especially fiber optics.