But you see it took the belief of the Son of God for the New Testament to take hold. All it would take is the belief of a Son of Allah. Remember, before the New Testament, God said put no other gods before me. It took a few deciples to convince people that Jesus was the Son of God. Many Christans were put to death over it but it finaly took hold.
Hmmmm... concept of something like the trinity in islam is a tough nut to crack indeed. To them, this concept is often interpreted as "shirk," polytheism, and a major sticking point.
Also, they're destiny (end of days scenario) is already written out for them, and they will be looking for the "great deceiver" and the mahdi. The Prophecy of the 72 sects works against this too, and would easily be invoked against belief in a "son of allah."
The Koran (Yusufali):
To be honest, IMHO, they are better off ditching Mohammads entire pack of lies and deceptions and open their hearts to an alternative message altogether.005.017: In blasphemy indeed are those that say that Allah is Christ the son of Mary. Say: "Who then hath the least power against Allah, if His will were to destroy Christ the son of Mary, his mother, and all every - one that is on the earth? For to Allah belongeth the dominion of the heavens and the earth, and all that is between. He createth what He pleaseth. For Allah hath power over all things."
005.072: They do blaspheme who say: "Allah is Christ the son of Mary." But said Christ: "O Children of Israel! worship Allah, my Lord and your Lord." Whoever joins other gods with Allah,- Allah will forbid him the garden, and the Fire will be his abode. There will for the wrong-doers be no one to help.
005.073: They do blaspheme who say: Allah is one of three in a Trinity: for there is no god except One Allah. If they desist not from their word (of blasphemy), verily a grievous penalty will befall the blasphemers among them.