I've played her on the PBE and i can safely say she doesn't fill the same niche as skarner or nocturne.
Her ult doesn't have anywhere near the same engage potential as nocs and is a pure mobility move. Her CC also pails in comparison to skarners lockdown.
Mobility wise she only has excessive mobility in places that she has already set up( usually her own jungle) and out side that her mobility is slightly below average.
Her sustained dmg is average for a bruiser, however if left unattended to gain a full fury bar her bite can devastate even tanks with damage comparable to chogaths ultimate.
While burrowed you retain full vision so she doesn't encroach on eves space either. She is firmly a beast all her own in the jungle and in team fights shes probably closest to darius in that she is a true damage time bomb who dishes out consistant AOE dmg around her while being fairly easy to kite.