This is simply stating that all things will be subject to God. Even the damned will be subject to God because in hell they are in a state of subjection to God's judgment upon them. It is God's will to judge those who are unsaved. It is according to His law and they will be subject to that righteous judgment. This verse does not state that the demons will be saved.
Reconciliation means to bring someone or something into a right relationship with another.
The lawful and proper relationship of the unsaved before God is damnation. Those who are condemned to damnation are rightly condemned and their relation to God is proper. They are eternally subjected to His judgment. The demonic horde is not in heaven. But, it is only the Christian who is redeemed.