TF, Eve, Lux, Kat, and Ryze seem to be the ones the Pros are picking in tourny.

A well played TF is super strong, as is a well played Eve (even after the nerf).

Those two get my vote.

I also really like a LB, but that's just because my duo partner plays a sick LB.

kat is broken

Generally every "AP assassin" will work good, as "AP mid". Keep in mind that now going full AD team is not punished enough (early/mid game you can counter by building Armor and choosing tankier heroes, but late game (when enemy will get their cleavers and whispers) you are kicked harder than usual).

I am not sure about Lux - she is mostly about killing squishie target in one of her combos from afar. Now with so many warmogs it is hard to insta-"long range burst" anyone expect support. It also mean that your not full combo gonna be less effective as warmogs provide very big hp regen. In qualifiers I remember seeing her 2 times: once she didn't done well, second time it was less than 30 min game.

Khartus was and will be good choice if you reach super late game.
Ryze doing good with new itemization.
Also dont forget your DFG - with so many hp and low resist it is very good item (in some cases almost crucial).
Keep in mind that any hero with "HP%" damage will also do well (Eve, Elise).

Orianna for utility, karthus for late game dps, kayle for dominating the lane and hopefully roaming, ad assassins for a similar reason.
TF as always stands out for pushing and roaming, anivia will push really well and prevent tower sieges from the enemy team from being too effective (same with lux)
Other than that, ryze for late game like karthus, works better against ad mids, ziggs has seen some use for the global ult.

Keep in mind too that most tops work well mid anyway, your mid really doesn't have to be AP.
(even all ad teams can work, just build tonnes of pen)

If I had to hazard what is going to become mainstream in tournaments, the AD casters will make their way mid, tanky AP casters will thrive in top lane, and the rest of the game will stay the same.