... Real question. Why ?
There is already an AP + Magic Resist item 
There is already an AP + Armor item 
There is already an AD + Magic Resist item 
... But where is the AD + Armor item ? Even an item with only 20-25 armor and 50 AD would be nice ( depend also of the passive/ active)
Rito tried before.
Wriggles: armor, AD, lifesteal, chance to deal bonus damage to minions/jungle monsters. Everybody built this. ADC, top lane, even midlane sometimes.
Madred's bloodrazor: AD, armor, attack speed, on hit 4% max health magic damage. Nobody built this except occasionally warwick.
Atma's impaler: armor, crit chance, 1.5% of HP as bonus AD. Was good when it was 2.0% of HP as bonus AD, after getting nerfed nobody built this.
It would have to be Melee Only and discourage Burst since then Ranged and Assassin champions could abuse it and hybrid offense/defense items, especially AD+Armor, have proven problematic in the past.
Seriously... when I'm going a bruiser or just really need some armor on AD champs it's a pain to have to build 2 items to satisfy that need.
Marksmen and assassins getting more durable than they need to IMO.
There was, R.I.P Atmas Impaler.
Because being tanky naturally resists burst damage. A tank's worst enemy is sustained DPS which, in LoL, is mostly in the form of phsyical damage. Of course there are some execptions, like 
or 
but generally the main way for a tank to die is sustained damage from the enemy Marskman.
Being able to build armor and AD in one item is very powerful because of this.
Because Marksmen would abuse it.
Halftime Illaoi10/25/2016, 7:30:09 PMit would be a must-buy first back item on all toplaners every game forever. It would be the new old triforce. The only way to counter it would be to play AP toplanes, which nobody likes.
Shoot, sunfire cape is only even kind of treading that ground and it's the sole reason top lane belongs in the garbage and nothing else.
