There's no rule that says you can't send an AP mid top.
And the standard meta is still only 1 or 2 AP carries, so by sending Talon mid and leaving top open for an AP carry, you can still follow the meta.
My only problem with Talon mid is that he's a counter pick more than anything. Sure, he can mid as he's basically an AD caster, but he's an assassin, and virtually ALL assassin champs are counter picks, not first pick material.