It wont matter. About the only way you could do that is to give them a psuedo auto attack that is in the form of a ranged spell, that is both spammable and easy on mana costs. This would end up being a problem tho because they would have to be able to deal more damage with spells then most other mages, as they would simply lose trades to auto attacks which they cant reply with. And they would be unable to use the low cd spammable one for harass most of the time as they would be forced into saving it to cs. The result would be that they would be OP once midgame came around and they flat out had more damage at their disposal. Or they would have to be extreme counterpicks to certain champions such as galio is and was to mages. They constant decision would be between farming and harassing where all other mages can do both. And if they had AOE it would push they wave which would hurt them far more then it would a ranged mage. Also running out of mana would be super pushing because they cant afford to simply walk up and cs. You would simply have a yasuo syndrome where a champion OP in lane against mages which isnt fun at all. The reason why assassins are typically melee is so that they are able to be bullied early in the game but reserve the right to all in traditional mages at later parts of the game.
Also I dont know what you mean by better autos. It doesnt matter how good the Auto is if its melee. The range hurts too bad.