The answer lies in the Holy Qur'an and the Ahadith:
42:11 "There is nothing whatever like unto Him"
Nothing is like Him. Therefore, no human form can take the shape of Allah Himself.
Should Allah reveal Himself, it would be too much for this universe:
Abu Musa reported: The Messenger of Allah (may peace be upon him) was standing amongst us and he told us five things. He said: Verily the Exalted and Mighty God does not sleep, and it does not befit Him to sleep. He lowers the scale and lifts it. The deeds in the night are taken up to Him before the deeds of the day. and the deeds of the day before the deeds of the night. His veil is the light. In the hadith narrated by Abu Bakr (instead of the word" light" ) it is fire. If he withdraws it (the veil), the splendor of His countenance would consume His creation so far as His sight reaches. (Book 1, Hadith 343)
(Sahih Muslim)
Let's not forget the story of Hazrat Musa (as). He asked Allah to show Himself to him, but when Allah showed just a tiny glimpse, the width of the tip of one's finger (according to the explanation by Ibn Kathir), then the mountain shattered in front of Musa (as), and he fell unconscious as a result of that. (Read Ibn Kathir tafsir on verse 7:143) No one has the power to withstand seeing Allah in this life. It is too much for us.
This verse is also saying that we cannot see Allah in this life, because it is possible. But, if a mountain shattered at only the amount of a fingertip of the glimpse of Allah, then what of a human being who wants to see Him? It is not possible to behold Allah. We are not made to withstand it. That is the answer from the Holy Qur'an. The Ahadith of Rasul-e-Karim (saw) also corroborates this fact. There is no way to get around it.
A weak human being cannot encompass the glory of Allah. Jesus (as) was a humble man and a Prophet as well as Messenger of Allah. He was extremely close to Allah and the closest to Rasul-e-Karim (saw) because of his high spiritual standing with Allah. However, no human being, and in fact, no human form can withstand the force behind the lifting of the veil of Allah. If He showed Himself, then nothing could withstand that power. Therefore, it is impossible that Allah ever would or ever did reveal Himself in human form.
No one can see Allah in this life, and no one can speak with Allah except by revelation, behind a veil, or by sending a messenger. Therefore, if Allah only speaks to us in these ways, then the only way that Allah would reveal Himself is through some sort of vision or dream, and not in a form which our eyes see things in everyday life, because obviously Musa (as) could not see him in that manner.
Adding to that, the Dajjal will claim to be Allah Himself, and the Holy Prophet (saw) said that no one will be able to see Allah until they die. Therefore, there is no possibility that Allah would come in human form to mankind. In fact, should this ever happen, it would be the Dajjal himself who would be this human deceiving mankind into worshiping him. So considering this expectation amongst Muslims about the Dajjal, this literal interpretation (which I instead take in a metaphorical manner) is the very reason why your argument could never prove fruitful since Muslims only expect a deceiver to try this, and not Allah Himself.
To add more to my argument, if Allah were to come in human form, it would imply that He had to have been born of a mother. Otherwise, who would believe that a human being is God? Yes, He could show signs of this, but many people would disbelieve in it thinking it to be magic. Not everyone believes in miracles, especially with the rise of Atheism these days. Miracles are so frowned upon, that they are considered a joke amongst many people in the world now. Sad to say. With that in mind, and Christianity being a joke in the eyes of Atheists, how would they ever accept someone who claims the same thing Jesus did, and says they are God Himself? People would call Him names and joke about Him. Is that part of the majesty of God to have people spit in His face? Astaghfirullah!
Allah is not subject to birth or death. "He begets not, nor is He begotten. And there is none like unto Him." (112:3-4) How can He be subject to birth when He is the First before anyone and everything, no matter how far back you try to go? Allah is always present, witness to everything. A human is limited, while Allah is not. How can He confine Himself when He is not confined? Allah is the Last after everything, no matter how far into the future you go, so how can you say He has an end when He can have no end?
The argument is very clear from the Holy Qur'an (which is based upon reason and wisdom), that it is beneath Allah to have to manifest Himself as a human being. Holy is He! Far above everything! After everything perishes, His face will remain. Can you say the same about Jesus (as)? No. Everything will perish except Him. Allah is far above having to need to resort to coming in the form of a human being.
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