Is wishing for the death of one's parents, which is an act of the heart, subject to punishment in this world and the Hereafter, and if so, what is its punishment in this world?

Wishing for the death of a parent is an act of disobedience (Uqūq). There is no specific prescribed legal punishment (Uqūbah Shariyyah) for this sin, but recompense is of the same kind as the deed. Thus, whoever wishes for the death of their parents might be punished by having a child who wishes for their death.