Splitpush for Days, teleporting and mhmm, this will be a annoying one.
Okay, after watching about as much PBE footage as I could find, I'm feeling better about her utility.
1. The tunnels? They're visible on the minimap to the enemy team, take ~2 seconds to stomp, and award gold for doing so. Also, stomping one destroys the tunnel, you don't have to get both. It's still strong, but even if they don't know where you are if they don't have vision control, they still know where you
could be that isn't an ordinary path.
2. Riot meant what they said about limited vision while burrowed. It looks like if you stood where blue buff spawns, you
might be able to see to the edge of the walls around it while burrowed. What this means is that, despite the movement speed and healing from fury, burrowing outside of the jungle, especially in places where you have no other source of vision, is super-dangerous, in part because of 3.
3. The sonar system actually looks quite balanced. There's a difference in size between champion and minion pings, but it's not incredibly obvious. Likewise, you can't tell who a ping is without getting into melee range or surfacing (if in a lane/open area) -- that person around the corner from you could be their 0/7/1 Jinx, or it could be their 12/2/7 Riven. It's Schrödinger's Champion, and if you open the door and get unlucky, you're probably dead. A lot of the deaths in the videos and streams I watched came from the streamer following and popping up at a champion ping, only for it to be someone who could easily solo them or two people moving very closely.
Likewise, with the tiny range of vision while burrowed, you can't see skillshots -- you can't even tell if the champion following you is one who has skillshots for you to dodge, or what sort of skillshots they might be, so you just have to juke and hope, because unburrowing is even worse: you lose your regen and movespeed buff.
That said, the champ is still absurdly strong by all appearances.