Most of us will agree on the fact that Sivir can put a lot of pressure and farm very well in a lane.
With her shield to absorb a potential deadly spell, a ricochet that can carry critics all the way to the opponent mid-laner and her ultimate for global roaming or escaping manoeuvres, could Sivir be and/or become a very strong pick in mid lane?
Best Answer
TL;DR : not a good idea, especially in soloQ/non-pro team
Every adc mid has to fill many criterias to be an actual midlaner, not just be good on this post.
Sivir could be a good laner indeed, but she doesn't have high poke/burst (like corki), tankiness (graves top for instance), or crowd control + poke (varus).
She is also very vulnerable to ganks because of her no-escape and this is why she needs a support.
She could be played mid indeed, but it will not be a top pick because of all these weaknesses, at least not in soloQ. You must also see the fact that she'll get crushed by any assassin and will never be able to kill any laner in 1v1 (in theory ofc, it depends on the level of the player but i'm judging on my actual elo which is around diamond 4).
So you could try it for fun, but she is not in the top tier picks at the moments for all these reasons.
Recap of the weaknesses : no escape(ult isn't an escape), no CC, no high poke, no 1v1 kill possibility, take the room of an assassin/mage.
Recap of the advantages : good push potential, good ulti in team fights, good damage late game (recap of recap : adc)