If the nonland permanent is an illegal target at the time Excise the Imperfect tries to resolve, it won't resolve and none of its effects will happen. Its controller won't incubate.
Exile target nonland permanent. Its controller incubates X, where X is its mana value. (They create an Incubator token with X +1/+1 counters on it and ": Transform this token." It transforms into a 0/0 Phyrexian artifact creature.)
: Transform this token." It transforms into a 0/0