They haven't been specific about exactly what it's going to be, but apparently it won't be like SoT.
This is the only official description so far:
'The Everwild team is focused on building an experience that allows for new ways to play in a natural and magical world. The development team, led by Executive Producer Louise O'Connor, is creating something truly original and incredibly special that aims to be more than just a new IP. Everwild will offer memorable, engaging and meaningful experiences for players everywhere to share. We cannot wait to share more with you in the future. '