Patch 8.7 means things will get a shake up. Although the patch focuses heavily on the jungle, there are definitely a few mid lane choices that have risen in popularity and success.
Ekko has crazy play making potential in the mid lane for a couple of reasons. He has extremely high mobility and burst damage while still having the safety net of Chronobreak to get out of sticky situations. Ekko can effectively assassinate an ADC in the mid and late game making him a huge threat.
Even if he falls behind in lane, which is hard due to his mindless wave push with Timewinder, Parallel Convergence offers the ability to AoE stun an enemy team and turn any team fight around. A skilled Ekko player may be hard to come by but is even harder to beat.
Lux is getting the buff to Final Spark that Riot was experimenting with on the PBE. While this won't make her laning phase much better, her team fights should be improved and her ability to constantly pick off enemies cannot be understated.
Lux was already in an alright spot but now if she can make it to the mid game her power spike will be much stronger.
Any champion that can build support items and still have damage is inherently strong. Karma provides so much utility for her teammates while still pumping out enough damage to be a reasonable threat from the back line.
Furthermore her laning phase is really strong as she has early wave push that many mid laners lack. Combined with Inspire to move around the map quickly Karma is a great choice for pushing in an enemy and roaming to help secure an early lead for her team.
Katarina is absurdly mobile which means anyone who can play her well is set up for success. While she doesn't have the strongest base damage anymore, it is still substantial around level three and gives her a lot of all in potential.
Anytime Katarina gets ahead, the game is typically done, which is why she looks to be even stronger in a meta where ganking junglers like Elise and Ivern are getting buffed and can help her snowball out of control
Ryze is still broken, even if his win rate on ladder doesn't necessarily reflect that. Ryze's damage is so high considering his low cooldowns and the reset mechanic on Overload. This allows him to easily chunk out or even one shot squishy opponents at almost all stages of the game.
His build patch also gives him a ton of power because he can build mana and magic resistance as a first item, both of which give him huge control over the lane and allow him to scale very nicely into the mid/late game.