What are Kronos's biggest open questions?

Kronos names its binding gates openly: the burner's plug-density requirement (n_p/n_c ≈ 16); cyclic fatigue of the high-field plug magnet; and, on the breeder, the confinement quality assumption (H₉₈ = 1.0) and the divertor's high radiated-fraction requirement.

Stating these as gates is the point: it shows the problems are understood and have defined closure paths.