I think Vayne is reliable pick in SoloQ.
The reason Vayne isn't seen in the LCS scene is primarily due to her being inferior to other picks in many reasons. However, in SoloQ where teams don't have enough chemistry nor communication, Vayne is one of the few ADC that can survive well against assassins if mechanically played right.
The stealth provided by tumbling during Ult is very strong in juking. Her ability to Tumble and dodge almost every skill shot is incredibly useful. A good condemn allowed my to solo kill countless Zed, Yi, Fizz, Kat, Talon in my games. Her W proc for the % health is his bread and butter for her to shred enemy Tank line without any ArmPen Items.