I gotta agree with Clamface and most of the opposition here.
The true strength of a Hybrid character is in the fact he makes use of two sources of damage readily, making it hard in the first place to get proper counter-play from him.
Another point is, Hybrid isn't technically a supported character type from Riot's point of view. Besides Gunblade and perhaps Rageblade, there are no real items that would sustain a "pure" Hybrid character, they always lean torwards one spectrum of damage, Magic or Physical. Heck, most of the "Hybrid" characters you listed only benefit from Magic Pen, despite them being able to stack AD for their skills, I think Jax would be the only real exception.
If a dual penetration item was to be implemented into the game, it would have to have nerfed stats from that of LW and Void Staff.
Why? Because first of all, it's going to be giving AP and AD. You can't have such an item otherwise, unless it gave some sort of hodgepodge stats like Nashors or Tiamat does. On top of that, you're requesting it give 35% Armor and Magic Penetration. This just screams abuse for anyone with dual stat stacking, yet relies on one type of source damage. Urgot for example, would pick this item up before a Last Whisper. Why? Because the AP would boost his shield, he'll still be getting some AD from the trade.
Secondly, what would be the counter-play of such an item? You're already behind when it comes to building resists, because you have to stack both just to counter that one Hybrid character, and stacking health does no good, because Hybrid characters tend to do a lot of damage.
So the curse of the existence of such an item would have to be either:
1) It's so weak that the characters it was intended for would get more bang for their buck building Void or LW.
2) It's so strong, it'll face abuse from any champion who has AD and AP stacking, or any Champion who has Magic and Physical Damage, while the Hybrid champions it was intended for get decent use of it at best. Heck, even some Mages would pick it up just for the Pen on their AAs.