Taking Taliyah mid is risky. Her "Q" is unreliable and easily dodged and quite frankly the range on her "E" and "W" is simply not far enough as using these abilities whilst laning against typical Mid champions (Viktor,Syndra) is extremely hazardous to your health as they will punish you for getting to close. That being said, I do really love this champ, and have gotten some awesome combos off with her in the past. The only suggestion I have is slighting modifying her Seismic Shove ("W") by adding a small stun upon landing, perhaps somewhere in the region of 0.7 seconds.
Let me explain.
Taliya's punishment potential for landing a combo on an opposing mid laner is pretty small. And in fact using her Seismic Shove to push an opposing champion towards you in order to get some harass off with her Q and E is dangerous against your typical assassin type characters. Take a Talon or Akali for example. It would be silly to Seismic Shove those champions towards you, as in doing so would mean potentially putting yourself in range of their kit. Seeing as Taliyah is incredibly squishy, you would mostly likely die :(
However by adding a stun to Seismic Shove, you would be able to get off an Unraveled Earth and then move out of range whilst casting a Threaded Volley at your opposing mid laner significantly increasing harass potential. This would mean that by landing a successful Seismic Shove, you would be able to punish the enemy mid laner just as they are able to punish you by landing their abilities.
I believe this small change would make Taliyah a much more viable mid laner as well as a more successful mid laner at higher ELO's