I hope you people realize that the introduction of Night Elf Mages as a playable race/class combination is because the Shen'dralar Highborne asked Tyrande to lift their exile and allow them to reintegrate into Night Elven society.
The Shen'dralar Highborne lived in Dire Maul if you didn't know. The Shen'dralar, under Prince Tortheldrin, imprisoned a Demon called Immol'thar and siphoned his Fel energy, granting them immortality. There were Warlocks within the Highborne caste. The Shen'dralar siphoned the energies of a Demon for thousands of years.
http://wowpedia.org/Quest:Shadow_Lord_Fel%27dan
"He is nearly more Demon than Orc by now."
Fel'dan is a demonic Orc due to his exposure and harnessing of Fel energy. Orcs don't live as long as the Elves do, and the Shen'dralar had spent thousands of years more than Fel'dan being saturated with the Fel energy. The Shen'dralar Elves weren't only Mages, there certainly was Shen'dralar Warlocks, Mages don't enslave or bind Demons and they don't feed off of their blood.
If anything it would make more sense if Night Elves could be Warlocks not Mages.
The Shen'dralar imprisoned Immol'thar thousands of years before the High Elves were slaughtered in Quel'thalas. After the destruction of Quel'thalas, the majority of the surviving High Elves renamed themselves Blood Elves and some Blood Elves started draining Fel energy from Demons, which caused the entirety of the Blood Elven faction to be affected by the Fel energy, their eyes becoming Green. All of the Orcs, barring the Mag'har Orcs, were tainted by Fel magic even an individual Orc has never directly consumed Fel energy.
You would think that if the Orcs and Blood Elves underwent a physical transformation due to exposure to Fel energy in a matter of months or a few years then the Shen'dralar Elves, who was exposed to Fel energy for thousands of years, would have features signaling demonic exposure.