It means that it is not possible that it can be executed or developed. That cannot be done or cannot be done. Impossible, unrealizable, useless.
That it is not viable, in its sense of "life" ("progression of existence") and "way" ("path, development"). See prefix in- ("negation").
Unworkable ( adj . ) 1- That it has no possibility of being carried out. 2- It refers to something that cannot be done. 3- Refers to something or someone who cannot be certified or qualified. 4- It refers to that pregnancy in which the baby has no chance of surviving after birth due to some malformation or any other cause.