Hybrid doesn't actually work in the game, at least in any way like how it has been implemented in the past. If you just have it as damage scaling from both AD and AP, there's little functional difference between that and pure AD or pure AP. Mixed damage is not a substantial addition to gameplay, as anyone who's played against Mundo or Shyvana can testify. If a champ has damage scaling on both AD and AP, people will usually find whichever scales better and stack the crap out of that.
The other challenge is that both AD and AP are heavily reliant on multiplicative scalings to reach their full effect. Penetrations, Deathcap passive, attack speed, etc. A champion encouraged to build both AP and AD won't be able to use those to full effects. That's another reason why even on hybridish champs like Kayle, Jax, and Akali, people build almost exclusively one stat. Kayle is probably the best example. Hybrid Kayle has always been mediocre, but pure AD Kayle used to be solid. After Riot slightly buffed her AP ratios, AD Kayle died, but pure AP Kayle saw a resurgence. We went directly from one to the other, with no hybrid stage in between.
It might be possible to make a hybrid champion where the AD and the AP serve different but complementary roles. A champion with AP ratios on utility scaling, who uses those ratios to stay in range while using their AD to damage their victim, perhaps. Realistically, such a champion would probably end up being built heavily in only one direction, but at least there's a choice. As it has been previously used, hybrid builds add little to the game, and require major finagling of game systems to make work. A third choice is no good unless it's in some way clearly distinguishing itself from the other two, and hybrid does not pass that test.