Taliyah does not have any lane assignment in champ select, making her hard to find. She should at least be under midlane, though I understand she has been jungled as well. To have nothing just makes her hard to find. Especially since there is still no way to turn off lane filter once you turn it on, meaning anyone with no assignments becomes unselectable.
You can custom set a champion's position in lobby by left clicking the champion and selecting the desired position for it from the drop down menu.
Default positions for champions are based on the roles those champions were played in during the last patch, not the current patch.
Sometimes champions fall so out of favor among players that they do not receive enough play to be registered for any position by the system.
Given the way the sorting system works, there needs to always be one role for a champion. Once you start role sorting you can't stop, so champions with no role actually become unselectable once you sort. Even if you search by name they can NEVER come up since it searches by name WITHIN THE CATEGORY and once you start picking a category you cannot ever turn off the category sort, only change category. Taliyah is currently effectively hidden inside champ select, so it's no wonder she isn't seeing much play. I wouldn't be surprised if large numbers of people think she was removed from the game.
