According to Rossi, San Jose likes Pettersson as a part of the Karlsson deal but the Penguins aren't comfortable including him. Pettersson is a legitimately valuable defenseman, so including him would be really challenging. But if the Penguins can find a Petry for LD swap somewhere (maybe Petry to Detroit for Chiarot?), I wouldn't have any issues with including Pettersson in a Karlsson deal.
Just spitballing, I imagine that would be something like:
Penguins get Karlsson at $8.5 million
Sharks get Pettersson, Granlund, 2024 1st and a conditional 2025 1st
That would leave the Penguins 2nd pair as Chiarot-Karlsson after the Petry for Chiarot swap.